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How To Calculate Muffler Size and Exhaust Pipe Diameter

If you’re a math wiz and/or an engineer, you’re probably going to like this article and the resources we’ve linked to. However, if you find yourself getting stuck (or bored) with the info below, here are the key take-aways:

1. The factory exhaust pipe diameter is usually a good choice for most vehicles.

2. The muffler manufacturers are doing all the math for us – no need to reinvent the wheel. If they say it will work for your vehicle, it will probably work for your vehicle.

Breaking Down The Problem

While we’re not going to go through and list out all the formulas and calculations you need to figure this exactly, we will break down the problem, explain how you would go about figuring things out scientifically, and then leave you with some good quick-and-dirty exhaust system math as well as some interesting links.

The science goes like this…

1) Mass of air that the engine breathes in + mass of fuel = mass of exhaust gases

Conservation of mass, right?

2) To calculate the volume of air the engine takes in, we multiply the displacement of the engine by the engine RPM and then divide by two (it takes two full revolutions for the engine to exhaust it’s entire air volume). We then convert that to volume to mass.

3) To make the calculations easy, you want to assume that combustion is perfect, i.e. there aren’t any byproducts, any unburned fuel, etc. It’s easier to assume perfect combustion and then “back in” to the actual numbers using an estimate after the fact.

4) Since you’re assuming perfect combustion, it’s easy to figure out how much fuel mass is added to the exhaust.

5) Once you know the mass of the exhaust gas, you just figure out how much volume that mass would occupy. Of course, you have to adjust for expansion due to the high exhaust gas temperature.

That’s it! Of course, when you sit down to figure it, you’ll find that getting a good scientific estimate takes a lot of work (which is why we don’t bother with it here).

Quick and Dirty Exhaust System Math

Easy Way To Estimate: Your intake system needs to flow 1.5 CFM per engine horsepower, and your exhaust system needs to flow 2.2 CFM per engine horsepower.

Good Way To Estimate: Take engine RPM x engine displacement, then divide by two. This is the intake volume. Use this same volume of air for the exhaust system, but then correct for thermal expansion (you need to know exhaust temps to figure things out).

Exhaust Pipe Size Estimate: A good section of straight pipe will flow about 115 CFM per square inch of area. Here’s a quick table that shows how many CFM each common pipe size will flow, as well as the estimated max horsepower for each pipe size:

Pipe Diameter (inches)

Pipe Area (in2)

Total CFM (est.)

Max HP Per Pipe

Max HP For A Dual Pipe System

1 1/2

1.48

171

78

155

1 5/8

1.77

203

92

185

1 3/4

2.07

239

108

217

2

2.76

318

144

289

2 1/4

3.55

408

185

371

2 1/2

4.43

509

232

463

2 3/4

5.41

622

283

566

3

6.49

747

339

679

3 1/4

7.67

882

401

802

3 1/2

8.95

1029

468

935

NOTE: These numbers are just estimates. All pipes are assumed to be 16 gauge steel.

The table above is probably over-estimating pipe size, but you can see that a 400 hp vehicle with a dual exhaust system only needs 2 1/4 – 2 1/2 inch pipes. Anything larger is overkill.

it was a very good article. i red and i was impressed. it solved my problem to make more efficiently exhaust for racing need. do you have any article about header? size of pipe diameter and how long it can be to give an optimum performance. i’m atuner from indonesia. an in my country, something like this was very rare. i have searched on the web, but found no article that make me delightfull to solve header problem. if you have some, it will make me very gratefull. thanxs before.

@ onyeh,
search for the haynes website and consider purchasing performance tuning for 4 strokes and performance tuning for forced induction. They are EXTREMELY useful and have a great amount of information for real motoring enthusiasts and professional tuners.

Brian – It can be either. Just remember that whatever units you use (cubic inches or cubic centimeters) must be converted to a unit of mass. My suggestion? Stick with metric. Conversions are much easier.

Great table but it may not be as accurate as you may think as i have a very quiet 3″ system on my 3.0L turbo Nissan skyline with 315kw@all 4 wheel, the problem is it’s 315kw on 15psi boost and 335kw on 19PSI boost, so did a google search for pipe size vs horse power

Very informative! I do not understand “overestimating pipe size”. Do you mean I can make more power with each size pipe in the chart? I have a non mandrel 1.75″ system on a Daihatsu Rocky that originally made 94hp with 1.5″ from the cat back. Am I properly sized, it needs all the HP and tq it can get.

Buz – The size of your exhaust system pipes should be matched to the power of your engine. So, if you have an engine that generates less than 100hp, the proper single exhaust tube size is 1 3/4″ . Smaller (like 1 5/8″) is probably just fine (might actually help with low end torque to got to 1 5/8″), but if you go much bigger you’ll actually rob power from your engine.

Also, when I wrote that our chart was over-estimating size, it means that the diameters listed aren’t exact. Instead, they’re rounded to the common exhaust pipe sizes so you can buy pipe…if we just used math to arrive at the diameter, we’d end up with some funky pipe sizes that would be impossible to buy. Hopefully that makes sense (the article is a bit cryptic).

Hi there Jason, Great reading, Im running a 572ci big block chev on a twin 2.5 inch system with an x pipe and flowmaster mufflers(620hp)primary pipe size is 2 inch going into 3 inch collectors i have been thinking about going to a twin 3 inch system but am wondering if i would see any noticible difference in the car as I seldom go beyond 4500rpm on the street(Max rpm 6000)the system is ceramic coated so cost a bit what are your thoughts?

Michael – If I’ve done the easy math right, your big block could pump out nearly 1,100 CF of exhaust per minute at 4500 RPM. If you’ve got a section of pipe that’s only 2″ in diameter, than you’ve got a bottleneck that’s probably restricting flow on your vehicle.

However, dual 3″ is a lot..I’m thinking dual 2.5″ or dual 2 3/4″ is probably enough. Based on all my readings and conversations with people who would know first hand, it’s better to be a little on the small side (2.5″) than too big (3″).

Jason, Thanks for the reply the only 2 inch pipes in the system are the primary header pipes(this is quite a big size primary pipe size as I understand) I think i will stick with the dual 2.5 system as its only a street driven vehicle (I do drive it hard often though)People comment on how awesome the car sounds it currently has Flowmaster delta 40 series mufflers on it but im thinking of trying out the super 44s as i understand they have a deeper tone than the delta 40s(Can you comment on this?)

I can’t comment on Delta 40 vs Super 44’s from experience, but I’ve heard the same thing. My honest opinion, however, is that you won’t notice enough difference to justify the expense. They’re both going to sound great.

Jason, So basically unless im going to run the car at max revs the dual 2.5 inch system will lose nothing to a twin 3 inch system ? and may even be better for low down torque (Although the car makes massive torque anyway) thanks Michael

Jason

Jan 10 2012

Michael – You’re going to lose something at 6000 RPM using 2.5″ pipes – the CFM requirements are higher than your current exhaust will allow at that RPM. However, in low to mid RPMs (4000RPM or less) you’ve got more than enough pipe capacity, and just as you say it’s actually a good thing to have smaller pipes in terms of off-the-line performance.

So, if you use the vehicle as described, than you’re better off with your current setup than a set of 3’s…assuming all the assumptions we’ve made are correct. 🙂

Kurt

Feb 25 2012

Hey Michael,
Your set up sounds nearly perfect! the one thing I can think of that will up your horsies across the entire rev range is to try siamesed pipes instead of a balance/cross pipe. Siamesed pipes are basically where the two pipes merge into one pipe for about a foot before splitting again. However on alot of cars it can be impossible to get room for two 2.5″ pipes next to each other at all!! Just a thought 🙂

thanks in part to the information you have provided ihave decided to go with a single 3 lnch exaust instead of a 2 or 2.5 inch dual setup all the information i have been able to find says i will gain torqe with a single 3 inch system thank you much

Hi there Jason,i’m running a toyota celica gts with rev at 8700 rpm,1796cc and the car has a valve lift at 5700 rpm.horsepower is 210,What is the best dimension for this car?the car has 3 inch air intake pipe from 2.75 and tuning ecu with lift from 6200 to 5700 and rev from 8200 to 8700 and my exhaust is 2,25 inch!!!nice article it helps my a lot but i have comfused…..

I recently bought a 1975 Mercedes 450SL as a classic but it idles rough. They have replaced plugs, fuel injectors and the catalytic converter in the exhaust system. None of this changed the rough idle. It wants to stall if the idle rpm is reduced below 1100rpm. Now they tell me that the exhaust manifold on the right side of the engine needs to be replaced. I understand that this car uses a “catalyst” as part of the exhaust manifold. Could this catalyst be blocked like the catalytic converter was thereby causing the engine to run rough? There is no missing at highway speeds or over 2000 rpm so I can’t quite grasp what role the exhaust manifold plays in this problem.

It’s been a few years that i last worked on a old classic merc.
Some of the fuel injection systems are trigerd by an old fashioned points system in the distributor, there s a block of them that comes out of the side of the distributor.
This may help, everyone overlooked the one i repaired and he had been to about 30 different mechanic’s including a merc dealership

I tried doing the math but I’m falling between 2.5″ and 2.75″. Was looking at 2.75″ system but would like your advice. I have a 4.2L V8 FSI with 420hp that redlines at 8250rpms. I plan on doing a few bolt modifications that will bring the car around 480hp. What is your suggestion?

HI Justin, See my discussion with Jason above im running 620hp on a dual 2.5 inch system so i think 2.5 inch max for you as a twin 2.5 is good up to 500hp I would run a twin 3 inch on mine if I was taking it to max revs but I seldom go about 4000rpm

Thanks for the response. Does the fact that my car redlines at 8250rpms make a difference? I did the calculations with stock numbers and im getting 610CFM which is right on the cusp on 2.75″. I usually shift between 3k-5k rpms but get close to the redline fairly often on my drives. (not a DD car) From factory, it comes with 2.5″ dual exhaust. Do you still think that 2.5″ max is right for me if I plan to do mods?

Hi Justin, I can see no advantage having a dual 2.75 inch system in fact most of the time you would be losing hp and definately low end torque, im making massive torque right through the rev range on a dual 2.5 inch but lose hp at max revs but then were comparing a 4.2L to a 9.3L im producing 500hp at 4000rpm and my system if great even at max revs your not producing more than 500hp. What size header pipes and collecters do you have ?

ok guys I need help . Ive got a 67 olds with a 350 ci motor and 455 edelbrock heads. motor should be pushing 460 to 500 hp. I want louad but deep sound and I want the best preformance i can get . if it matters ive got a set of hooker headers on it now. what muffler sould I go with and what size ? and should I go center to center or a off set chambered muffler….. I wandt the sound
thanks guys

Kyle – You can calculate size by looking at the CFM figures on the mufflers or contacting the manufacturers. As for offset vs center to center, I don’t think it makes much difference…but if I had to choose, I’d go center to center.

The sizngs are so incorrect it’s not funny.. my car has about 270hp stock and has a 2.5″ with a crush axle back.. even a better (catless etc.) 2.75″ exhaust is good for 330-350hp N/A.. should see 350 *W*HP out of the OEM exhaust even with forced induction.. and that’s with cats in the headers and 4 cats total -_-.. Evo’s run 2.5″ up to about the same and even a single 3″ is fine for 450-500hp

admittedly the OEM exhaust i run is twin 2’s (or 1.75 or something) off the headers into a single at the diff.. but still. you should mention more about the design not neccessarily needing a consistent piping size to the end like this.

Sir,
I m interested in silencer . but I am having very little knowledge about silencer . I don’t know how to calculate pipe size and holes maid on pipe of silencer and how to calculate the chamber in silencer and all regarding silencer . I m having esteem car . and I have to modify the silencer and make it more silence instead of noisy . can please guide me for this silencer developing and if there is a book covering my requirements can you please suggest me . I will be thankful to you .

hi,i’m looking into a catback system and i’m looking at the chart and were it shows the max hp for a dual system is it true dual from the manifold back with 2 converters and 2 mufflers or is it dual catback?

thanks jason, so are we to assume the chart is assuming the flow rate using just straight pipes not taking into account it has any converters,mufflers or am i just totally missunderstanding the chart altogether?

Kirt – The chart shows you what approximate size of tubing you need for a specific engine HP, based on the amount of exhaust gas an engine typically produces for any given HP. Since it’s based on the amount of exhaust gas that has to flow through the tube, mufflers and cats don’t matter…it’s just flow.

Think of it as a water pipe – a 1″ pipe is only going to flow a certain amount of water at any given pressure. If you want to flow more water, you have to make the pipe bigger. It also doesn’t matter what you put on the pipe anywhere in the line either. You can add valves and tanks to water pipe, but those things aren’t going to increase water flow because the only thing that matters is pipe size. Make sense?

So i was wondering what formula did you use to get the pipe area. I want to see what the larger diameters flow. I may have to use a 4″ exhaust to achieve the power goals that i want but i wanted to do the math to make sure.

Jason 2 – Sorry man, I don’t have a simple formula to calculate flow by diameter. It’s actually quite complex, which is why it’s not listed here. If you’re looking for an easy way to calculate pipe area, it’s Pi times the square of the radius (remember Pie – R – Square from school?) 🙂

Hey, ok so I’m not fully understanding, this but I’ll tell u my set up and maybe u can help me! I have 2008 dodge ram 1500 with a 287ci motor stock hp 310, stock tq 330 but I have about 40 hp/tq extra of bolt ons. Now I installed a 2.5″ pipe to a y pipe to twin 2.5″ pipes going to five inch tips. I don’t know why but I personally feel like I lost hp/tq after this install? Would it be better to just go single 3″ since I’m steady adding more performance parts also is why I’m asking I’m not trying to rob performance, over sound? Hope I explained this good enough, thanks Donald

I HAVE MORE OF A QUESTION, I HAVE A 99 DODGE DURANGO AND INSTEAD OF THE PREVIOUS OWNER PUTTING THE CORRECT SIZE MUFFLER ON IT HE WENT WITH A MUFFLER THREE SIZES SMALLER. SHOULD I CONTINUE WITH THAT OR GET THE CORRECT SIZE AND WHAT IS THIS DOING TO MY TRUCK?

I have a stock 4.8 gmc sierra with 2 3/4 pipe exhaust. I has told the muffler robs my truck of mpg and horsies. I want to put a new muffler only on and can’t find any after market exhausts that are 2 3/4″ should I replace the muffler with a 2.5″ or a 3″ and when doing so should I keep the 2 3/4″ tail pipe or replace to fit the new muffler. will going from 2 3/4 pipe to 2.5″ higher flow muffler back to 2 3/4″ tail pipe work?

I’m currently in the process of swapping my 97 Civic 1.6L SOHC engine to a 2.0L DOHC engine approximately (170hp @ the flywheel) and I am in need of a custom exhaust but I want it to be a very quiet exhaust. I will have a header with a 2.5″ collector and I was thinking I could go with a 2.5″ non-mandrel bent exhaust (essentially 2 1/4″ right?) into a restrictive muffler to keep it all quiet. Would it be best to go with a multiple baffle muffler or a turbo style muffler? Also is my exhaust size right or should I smaller or larger?

Jason – Your plan sounds good to me. I might think about going with a slightly smaller pipe (2.25) that was mandrel bent simply because a smaller pipe will perform better…part of what you’re trying to avoid is having the exhaust gases cool too quickly. If you go with an oversized pipe (even if the bends are a little smaller), you’ll get some of that negative cooling effect you’re trying to avoid. This can reduce low-end power.

As for muffler style, I don’t have any guidance other than to look at Hushpower mufflers. They claim to be quiet yet still high performance. The trouble with after-market mufflers is that they’re almost always loud.

I can get crush bent exhaust for a very good price. Would I hurt my fuel economy and/or power production too much by going with 2.25″ crush bent piping with an 18″ inch resonator and a 2.5″ oem replacement muffler (since it’s going to really restrictive)? Or should I go with mandrel bent exhaust at a bit more costs?

Jason – There’s not a HUGE difference between crush-bent and mandrel-bent tubing, but mandrel-bent is always better. I’d say go with whatever makes the most financial sense, especially if you’re going with the OEM muffler.

I have a question. Ive built a 4 cylinder MGB GT engine 142bhp@ at the back wheels, its a very tuned engine std they were 95 at the flywheel which probably gave 65-70 BHP at the back wheels. Im currently running a 2″ freeflow system with a rear muffler (Moss Tourist Trophy system). Id like more of a low down throaty sound (MG`s tend to sound like farts in drain pipes).

Would a larger backbox help? Or would that two box system have helped with that? Perhaps a 2.5″ system would have been better?

I chose the single back box as I had read somewhere that the rear muffler gives more throat and the front creates a higher pitch?

Ray – The very best sound I’ve ever heard out of a 4-cylinder exhaust is fairly muted and likely restrictive. If you’re looking to get good power AND good sound, I don’t have any ideas. I’m not aware of any tricks to make a 4 or 6 sound like anything other than a 4 or 6, at least outside of idle.

I currently have a CRV engine going (approx 170hp at the crank) into my 97 Civic and I was considering a custom dual exhaust (1 3/4″ or 1 5/8″ into a dual inlet and dual outlet muffler. Would the dual exhaust help quiet my exhaust any?

Jason – Probably not. The frequencies that generate the most noise aren’t really attenuated by additional tubing. I’d also say that you’re trading exhaust noise on just one side of your vehicle for noise on both sides.

If you want to reduce noise, a good trick is to point your exhaust tip(s) down towards the ground, and to run them out of the side (behind the wheel) rather than straight out the back.

Jason – If I understand you, you’re contemplating a custom dual inlet and/or dual outlet exhaust. I’m also guessing you have a V6. A dual outlet won’t be any louder or quieter than a single outlet if it’s coming from the same single muffler (see my previous comment, where I was assuming you had a 4cylinder). As for a dual outlet coming from two separate mufflers (i.e. a “true dual” system), than a dual exhaust will probably be harsher than a single.

This is because the V6 exhaust note is inherently unbalanced, as opposing sides of the motor are detonating an unequal number of cylinders at any given time. Therefore, splitting this exhaust up into two completely separate tubes is going to give you a raspier, harsher sound than you’d get from balancing both sides by running them into the same muffler and/or using an x-pipe.

Based on the fact that your vehicle has a relatively small V6 (I’m still wondering if you have a 4cylinder, quite honestly), I’d run a single muffler, single exit exhaust system and then just try to buy a good muffler that isn’t too loud. Hushpower is supposed to be a quiet performance option, but I don’t know if they have anything that fits your CR-V. Good luck!

P.S. If you have a four cylinder, there’s nothing to talk about here…single in and single out is the only way to go. Anything else would be silly. 😉

My line of thinking is that if I split my exhaust after the header then I have smaller pipes which in return I think should be quiter then I add two resonators which in return makes it even quieter then I can two mufflers to each pipe and now it’s even quieter but I was also thinking that I could run both pipes into a dual inlet and outlet muffler and hopefully still keep a quiet exhaust.

Jason

Dec 17 2012

Jason – As I’ve said, there’s no benefit to extra tubing. One resonator and muffler will work just as well as two. It’s not a “bigger is better” situation because a 4 cylinder doesn’t pump out enough exhaust to require two of anything. You’re over-thinking it. 🙂

Jason

Dec 17 2012

I think you misunderstand because I’m thinking smaller pipes versus one larger pipe. Your chart shows that two 1 5/8″ pipes flow the equivalent of one 2 1/4″ pipe and the 1 5/8″ is what I’m getting at.

Jason

Dec 19 2012

Jason – I’m not misunderstanding. You want to take the single exit on the stock manifold, split it in two, and somehow reduce the noise level without effecting performance. Unfortunately, it just doesn’t work that way – one pipe (and one resonator and one muffler) is all you need. No amount of tubing is going to reduce noise any further than a good muffler (the frequencies that are attenuated by extra tubing aren’t impactful on overall sound levels), and whatever extra tubing you add will likely hurt performance too (if exhaust gases cool too quickly, you’ll kill your low-end torque). Don’t screw around with it – focus on finding the best muffler you can.

rob

Dec 19 2012

so explain this to me please anyone. if these car geniuses calculate this the why does my suburban and dakota have stock 3 inch exhaust. suburban 454 about 350 hp. understandable. dakota 3.9 v6 180 hp. shouldnt there be a 2 1/4 to maybe 2 1/2 in. please explain.

Rob – Who knows but a Dodge engineer? I could guess that a) only the tip is 3″ or b) that the pipe size from the manifold to the muffler inlet is much smaller, but the fact is I have no idea.

If it helps you, Chrysler is a three-time loser. They went under in the 80’s, then went under in the early 2000’s when Cerebus Capital bought them out, and then they needed a federal bailout. Chrysler didn’t fail on three separate occasions just because they had some bad luck…

thats why the dodge costed 500 bucks. its 3 inch from manifolds to muffler and 2 1/2 out. i kinda wanna do a 2 1/2 all the way through but really how much money do i want to throw away. i mean dodge really isnt what you want to tell people you own but the fact of the matter is its 4×4 and works good 92000 miles and no mechanical problems. MIGHT last another 8000 miles.lol.

Hi
I was just wondering, I have 2000 Mercury Grand Marquie that I bought used but in great condition with only 140,000KM on it. I installed a K&N recommended custom cold air intake with shroud and I also installed a Helix throttle spacer on the throttle body. The car came with a single exhaust from factory so I had a custom dual put on by the performance shop in my area. We cut the original Y and made 2 separate exhaust by adding the left drivers side. We put a regular muffler on the left side and kept the original on the passenger side. The performance was excellent and the car would squeal the tires even with the traction control engaged. We kept the pipes and everthing normal diameter. I missed my performance mufflers ( magnaflows ) that I had on my 1993 mercury 4.6 ltre that I finally scrapped at 357000km. I decided to put the same type magnaflows (tube type) on my 2000 Mercury. The car sounded really deep in tone but when I started driving for about a week I noticed that I didn’t have the same power and my fuel consumption increased. Is this because of not enough back pressure? I am seriously thinking of going back to the normal standard mufflers if this is the cause. The performance guys say sometimes you comprimise power for nice sounds but I am not sure? Any ideas would help. Car runs perfect otherwise. Thanks Darrell

Darrell – There are a lot of reasons that you could feel as if your car is slower and getting worse gas mileage. First, it’s the winter time, which means that fuel economy is always lower (cold engines are less efficient, and winter fuel mixes aren’t as good as summer fuel mixes).

Second, the “butt dyno” – i.e. your personal assessment of power – just isn’t very accurate. It’s hard to tell how fast something is just by feel.

Still, any time you hack together an exhaust system, you risk creating something that doesn’t perform as well as the stock system. This is why I recommend either a) going with a quality after-market cat-back kit or b) working with an experienced performance muffler shop that knows about tuning.

If your current muffler shop says that “you have to compromise power for sound,” find a new shop. That guy couldn’t be more wrong.

Hi Jason.
Thank you for the reply. I just wanted to give you a little more detail to avoid confusion as maybe I didn’t explain enough. The guys that did my 2000 Mercury Grand Marquie are the same custom shop that did my 93 Grand Marquie. They have been doing every type of car out there and have a great reputation as far as their work and critical details involving all their installations. All their systems are welded and in most cases better than factory. They do not install junk but only top of the line products. The comment about sometimes you sacrifice a bit of performance when you change some of the original factory equipment. They did all of this work in the summer and even though the 2000 Mercury I have now feels much quicker than the 93 Mercury, I only seemed to notice the feel of the car being different since I went over to the recommended Magnaflows that were installed. Is it possible that because the 2000 Mercury is more solid and quiet that when I switched exhaust I became more aware of the engine sound which I never really heard with the factory single exhaust. I know when they installed the duals they cut off ( which seems to be standard ) the damper weight that was just after the Y. When the duals were installed and perfectly matched except for an additional new standard muffler and the original factory I was getting a vibration at idol in Drive with the brake on. The opinion of a few custom shops was that I shouldn’t need these weights and even they cut them off when they insall duals. My performance shop thought it could be because of the mismatch between mufflers. I bought new weights and had them installed on both sides of the duals and this solved the problem. I don’t know if the match mufflers would have made a difference without the weights as I never bothered after the problem was gone,
My 93 Mercury also had the original 4 converters removed and we put on the mustang cats (only 2 ) and then took everything to the xpipe and then to the magnaflows (oval ). My 2000 Mercury sounds really good right now but I don’t know if some back pressure is needed as they say most of these cars have tuned exhaust when they are designed and is there any possibility that maybe I have disturbed this equation since installing the magnaflows? Jason I am just trying to figure out if it is me or has the car lost some additional punch that I noticed when I went from the duals ( standard mufflers to magnaflow tube type). We also added an H crossover connection between left and right but it made very little difference. If you get to know how a car runs and feels as we all do after time I’m sure if something changes you will notice it. I felt right after I drove the car away from the performance shop that it just didn’t seem to have the same snap. ( Maybe I’m just losing it but most of the time I have always been correct when something changes in the characteristic of the car that I am use to driving ). This definetly changed something but no one ( other shops ) have any idea? I would like to know if any of your members have ever come across something like this when they modified their cars from muffler changes be performance or otherwise! Thanks Darrell Smith Toronto.

Darrell – I hear what you’re saying, but in all honesty I’d find another shop. Here’s what I know:

1. There’s very little reason that removing the factory exhaust and replacing it with after-market components should reduce power. At worst, it should make no difference…and on a Crown Vic/Grand Marquis, you should be able to add power with an exhaust relatively easily. This “sometimes you lose power” comment is alarming.

2. Connection quality (i.e. how great they weld things) has very little to do with tuning ability or performance.

3. Adding an H-Pipe to a V8 makes absolutely no sense…if you’re trying to get rid of a vibration you could try it, but I would focus elsewhere first.

4. If your car felt fast when you first had it, and is now slower, it could be that the mufflers have become clogged. Did they check that?

5. Swapping out the stock catalytics for Mustang catalytics doesn’t make a lot of sense to me either. Modern cats aren’t very restrictive at all…unless you’re strapping a supercharger onto the engine, you don’t need to touch the cats.

6. There’s a whole lot of rigging and trying going on…good shops don’t need multiple tries to get it right.

Again, for almost all the reasons listed above, I’d say your shop isn’t very experienced. I’d contact your local racing clubs and ask them for a recommendation.

Hi Jason.
I guess there is still some confusion with my explanation so I will try to simplify what has been done.
Just the 2000 Grand Marquie
1. Car was bought with factory single exhaust and was very responsive.
2. Added K&N cold air intake complete kit in summer (good response in performance and much improved.
3. Added Helix power tower to throttle body. (better mid range acceleration)
4. Had factory Y pipe cut and kept original factory right side exhaust complete and factory weight damper was removed.
5. Had left side exhaust installed without H pipe just straight through.
6. Now car had dual exhaust with no H pipe and the only thing different was original factory muffler on right and a new satandard muffler on left side. Car was responsive and only thing that changed was that at idle and in gear there was a small vibration at a certain frequency when stopped,
7. We installed the H pipe at my request thinking that it might help the small vibration but didn’t.
8. I decided to buy the left and right damper weights from Ford dealership andd had them welded on in the same place as the original factory exhaust.
9. Problem solved vibration gone!
10. Car running very well and performing excellent and very responsive accelleration.
11. Missed my nice Magnaflow sound so in about a month later I decided to install the new magnaflow tube type reccommended by Magnaflow for my car.
12. I got to hear them before they were welded in place and was very impressed, Low nice rumble but much louder if you hit the pedal.
13. Drove away after every thing completed and felt the car sounded great but it seem to lack the same punch. I thought maybe it is just me adjusting to the new system but again I can’t explain why the car just doesn’t feel the same.
You are correct in the fact that you can’t measure power and speed from your butt and I’m thinking maybe it’s the difference in the acceleration noise between original quiet mufflers to the magnaflows.
The comment about sacrificing power for sound was taken wrong. What I mentioned to one of the installers was that I felt my gas mileage was a little worse than before with the factory installed single system. His comment was more that like any HP improvement
sometimes you have to sarifice a little more fuel to get more response which makes sense.
I have a lot of respect for these guys and they do have an excellent reputation and I probably drive them a little crazy when I ask them why the car just feels slightly different since all the work. They even test drove it and inspected all the work and said it was running very well for a Mercury Grand Marquie and couldn’t see any problem.
I still love the sound so I don’t want to go back to the quiet mufflers. I also know Grand Marquies love cold weather and perform very well the colder it gets and yes fuel burns better in summer for sure.
Thank you Jason for your feedback and like I say it may just be me.

regards Darrell

p.s. A very Merry Christmas to you and your family!

Jason

Dec 27 2012

Darrell – I understand more now. It sounds like you had a semi-customized factory exhaust that you replaced with two high-flow mufflers.

If the Magnaflow mufflers you added were designed for a single-exit exhaust, they’re likely too big for your dual system. THAT could cause the performance to fall off a bit.

Patrick

Dec 27 2012

I’m having to have a custom exhaust done to my car which will be making around 175hp around 7500rpm. I want a quiet exhaust but not too restrictive. I was thinking about going with an oem type muffler but I figure it will bottleneck the whole exhaust.

Would it be best to go with a 2.5″ piping out to a restricitive 2 1/4″ muffler or go with a 2 1/4″ piping out to a 2.5″ muffer? In other words where’s the best place to put my exhaust restrictions nearer to the header or near the rear at the muffler? Oh all piping will be crushed bent so the actual restriction size will be smaller.

Patrick – If we’re talking about a quarter-inch here or there, it’s not going to matter. I would go with a mandrel-bent system, however, as that does matter. I’ve seen data to suggest mandrel bending is just as important as finding the right size.

My general guidance: the factory exhaust system tubing is very close to the right size. When in doubt, stick with the same size.

very interesting. but how about pipes below 1.5 inches. im building a header for my 1.3l ford aspire motor. and i want it to be maximized for cruise rpm. i know your pipes hp rating were for max hp numbers, and cruise hp numbers are maybe 1/3 of the rated wot for that specific rpm. any idea on what size i should run for my primary pipes?

i cannot let myself believe that factory exhaust is maximized for cruise on any car. we as americans want to go fast, so our cars are designed with flowier than effienct exhaust systems. i may just have to do this test myself with some sort of pipe sizes, like 1.2, 1.1. 1. .9 and .8 inches. itd be a blast building 5 different but similiar headers like that. do you think those size primaries could get me the results that i need. reading about that tri y design got my hopes up a bit on wanting to try that on my car for fuel economy. in that case, can lower torque are lower rpms get me better fuel economy?

There are a lot of factors that go into header design besides tubing diameter.

My suggestion is to find a successful header design on a similar yet larger engine, then scale it down. If you try a bunch of different diameters without considering other factors (tube length from head to collector is really important), you’ll be spinning your wheels. 🙂

bryanh actually jason is correct. the stock pipe is optimal for less than max hp. the factory stuff is meant to maximize power for normal driving conditions. although if you still build those headers would you be so kind to post those results so we can see what works and what doesnt? losing hp and torque doesnt mean you will lose gas mileage. alot of the reason people lose mpg with better hp is because the lead foot that comes with the power.

Having got caught up with all the “bigger is better” hype I went with a 3″ dual (with x pipe) exhaust system on my full sized chevy Caprice. I built a 355 SBC that made 400 flywheel HP on the dyno and have a set of tri-y headers with a 2.5″ collector. The system has already been purchased and installed on my car. After reading lots I have a terrible feeling that I made the wrong choice on going with 3″. For one, the car is too loud for my tastes. I actually have a pair of resonators on order that I am going to install in hopes bring the volume down some. Hindsight I would have gone with a 2 1/2″ system, but I dont want to spend another $800 on exhaust.

Taylor – The headers are probably going to impact you more than anything, and they don’t sound like a bad choice. However, the only way to know what impact the dual 3″ pipes have is to test the vehicle with 3″ pipes and then 2.5″ pipes and see the difference. My guess? You’re losing a little bit of low-end torque. How much is hard to say.

Jason, between the headers and crossover the pipes are removable. I believe the drivers side is ~2′ and the passenger is 1.5′. Would it be be beneficial to knock these down to 2.5″ before the 3″ crossover? I picked the headers as they have good low end and midrange power, just not to sure why I went with the 3″ now that I think about it. The guy that manufactures the headers and exhaust system usually recommends people switch to 3″ around the 400FWHP mark. Live and learn I guess…

taylor – First of all, cats don’t effect performance nearly as much as people think they do, especially if you purchase racing cats.

As for dropping to 2.5″ before going to the crossover, I’d suggest getting rid of the crossover unless you’re trying to mellow out the exhaust note. Its not necessary on V8’s. That way you can run the right sized pipe all the way.

Still, if this system is all done, I don’t know that I’d bother. The slight loss of low-end torque isn’t going to make much of a difference on the street.

Thank you for your input Jason. And here I thought the crossover was the “way to go”… I think I will just leave it and the next time I build another car will do my research before hand rather than after!

Frank

Feb 11 2013

Hello
Love the topic and conversations i have read!!!!!
My question is on a 99′ regal gs 3.8 s/c. Currently stock, but finally have the money for mods. Car is rated at 240hp 280tq, planning on getting custom pcm, ported throttle body with spacer and a whole bunch of little stuff to help reduce the common knock retard issue with this engine. Planning on doing full exhaust, front p log to replace manifold, rear ported manifold, crossover tube, they offer a 2.5″ and 3″ down pipe with and with out cat, prob gonna go with out out cat and an o2 simulator. The only full exhaust replacement i can find is 3″ stainless with muffler and resonator optional. Will probably go with the resonator to kill that annoying rasp 6 cyl are known for. What do you think of the 3″ down pipe with 3″ mandrel bent exhaust, i will be running a smaller pulley not sure what size, guess it depends on where i go with the exhaust. I can buy all the bends and do a 2.5″ exhaust and get the 2.5″ downpipe…….after the mods prob lookin 330hp but with forced induction not really to sure how the math equation helps…..guess i will be around 12 psi, stock is at 8psi and im not sure what size factory exhaust is either. I do know the factory down pipe is extremely restrictive and just that swap alone is good power gains. What do you think……

Frank – There are lots of questions there, none of which have easy answers. Going with an after-market downpipe is smart, but going with a 3″ vs 2.5″? No idea. You can’t really trust the downpipe manufacturer’s dyno testing, but that’s probably what you’ll have to do to get an answer to your question.

As for a single 3″ tube system, I say go for it. That seems about right for a forced induction motor pushing 300hp.

Mihir – I don’t know if tubing thickness has much impact on drone…I’m sure there’s an effect, but I’m not sure that it’s the most economical way to solve these problems on a car (thicker tubing is both more costly and heavier, so using it for an entire exhaust system is economically out of the question).

However, many vehicle exhaust systems are 16 or 18 gauge steel, and I’d guess that this is a good thickness.

I have enjoyed visiting your site and reading your thoughts. I have a Q for you. I own a ’92 Ford Ranger w/ the 2.3 L, 4 ( and I LOVE IT )! It came w/ a single 2.25 pipe on it. When that wore out, I replaced it w/ a split/dual cat ( 2 pipes @ 2.25″ ) back system and a FLOW MASTER 40 muffler. I desired the look of the “functional” pipes as well as the deeper, and louder tone.

It sounds GREAT when idling and cruising but, when I “get on it” it trumpets because it’s a stock, non loping 4! I am getting ready to lift the body to make room for larger tires. This means, that the exhaust system will have to be adjusted so it looks good again.

This is the time to make mods! I want to use a HOOKER AERO FLOW muffler and 2, 1.25″ pipes. The engine rarely turns above 3000 rpms ( it has a 5 speed ) and am seeking more low-mid power gains.

Later this year, I will bore the throttle body, spacer, port and polish the intake manifold and install higher PSI fuel injectors. This will increase the flow into the motor. Do you think a larger 1.25″ pipe, might be a better choice?

Thank you for your time, just reading this Long Winded letter! I look forward to your input.

Alan – If you’re most concerned with low-end power, than 1.25″ pipes are likely fine no matter what you do. I’d rather have a smallish system on a rock crawler, b/c smaller pipe diameters create more of a scavenging effect at lower RPMs…they just rob HP at higher RPMS. So, I’d leave it alone if I were you. 😉

PS: In the letter I sent you a few hours ago, I think I may have said, going to a smaller 2.25″ 2.50″ exhaust pipe size. I meant; 2 @ 1.25″ or 1.50″ w/ future performance upgrades. Sorry for the confusion.

I have a colt rodeo 2.4 i (4g64) engine . viper branch 4into1 , and 50 mm pipe with free flow. it has lost power since putting the 50mm , and seemed to be a bit heavy on fuel. it had a 48mm pipe before . would this 2mm make such a difference? what size U recon / the 48mm sounded great and had good low down torque

Brian – Can’t imagine that 2mm would make such a big difference, but if that pipe included a new header, than all bets are off. Changing the header/exhaust manifold can make a big difference, especially if the header/exhaust manifold is tuned for top-end performance.

jose – I’m not sure if the system you’re looking at is worthwhile or not, but there’s nothing about the description that gives me pause.

However, I’d hesitate to buy any system that didn’t come with some sort of expected performance improvement and a dyno graph to support that claim. Meaning, they should say “our system adds up to 10hp – here’s a dyno sheet to prove it.”

I had a muffler shop splice in a pair of 2.25in magnaflow (11225) on my 2012 mustang 5.0. The pipe is 3in duals but he said I had less than 2.5ID. I know I have a pair of 2.25ID resonators as well. Did this guy just give me one heck of a bottleneck or should the mufflers be ok with my 412hp?

That’s good to hear. I’ve noticed an increase of lower end tq but haven’t had a chance to make runs or test the top rpm range yet. I do enjoy the added lower end though! Thank you for the info and piece of mind, it is greatly appreciated!

You probably dont remember, but you replied to my comment awhile back. I have a regal gs with the 3800 series s/c, currently stock. We talked about a full 3″ mandrel bent system from manifold through tailpipe and decided sence there was boost involved it was good to go. Do to finances i had to cancel full 3″. From the resonator back it is 2.5″. The down pipe is the most restrictive part of exhaust along with a u bend that was designed for 2nd o2 sensor just past the cat. I ordered a true 2.5″ downpipe without cat and an o2 simulator. I was thinking instead of the 3″ downpipe being knecked down to 2.5″ it would be just as benificial just having 2.5″ all the way. With the pulley ill b putting out 11lbs of boost. This should b an ok setup? I really dont have any plans on very much more, except for the 4″ cai and custom pcm currently on order and mayb a throttle body soon.

Frank – Sounds good to me, but I’d recommend posting this question on a forum for Regal GS (or 3800 S/C) vehicle owners to see if anyone has any specific insights. However, as a general rule, 2.5″ vs. 3″ isn’t likely to make a big difference in the way your vehicle performs on the street. If anything, it will perform better at the lower RPMs with this setup.

It is an interesting topic, But i have a feeling that it does not take into consideration for backpressure that are needed in non turbo petrol cars(too low backpressure = damanged valves and loss of HP). I am currently “making” my own custom, exhaust for my 206 2.0 GTI 159bhp@6700rpm(with the old worn out system) and are wondering if a 2″ is not better than the 2.25″ after the race cat, for the sake of backpressure and decreased volume of the colder gas? Or am i completely on a sidetrack here?

Kim – It’s not really about back pressure, it’s about exhaust gas velocity. The heads and ECM are tuned for a specific ideal velocity, and your goal is to make sure the exhaust system hits that ideal velocity figure at the point you want it to.

Quite frankly, the headers/exhaust manifold is far more important here than the exhaust tubing. Does your header manufacturer have a recommendation? If not, you might try to match the size of the stock system, test it, then increase diameter and test again. Testing is the only way to know for sure, as I’m not aware of any good (yet simple) methods for calculating the ideal setup…only if you had the right modeling software like the exhaust system manufacturers do, I bet you could get very close.

Ty for the reply,
You are right, there probably is not any easy way to find the proper backpressure, it is a topic i had no luck finding good info about.
The header i am using is slightly a modified 4-1 from supersprint(from old system), to fit the cat and middle muffler piece. I have a feeling that it is pretty optimal for the car.
I am still unsure if 2″ or 2.25″ is better, but for now i welded on a original middle muffler and it has a 2″ exit pipe.
If i can get info on if a bigger diameter can give alittle more bang for the buck, ill probably swap it to 2.25″ 🙂

Jason, I see where you said “A good section of straight pipe will flow about 115 CFM per square inch of area” but how do bends in the exhaust pipe such as where it goes over the rear axle affect flow? According to your chart I have my exhaust pipe sized pretty close (460 hp into a dual 2-1/2″ system with an X pipe). The pipes are also mandrel bent. Do mandrel bends present any appreciable back pressure to the system that could skew the results shown on your chart? If so do you think going with a larger pipe (such as a 2.75″) would make up for it, or might that cause turbulence? What are your thoughts on a H or X pipe? Do you think they lower system back pressure any due to each side now having 2 exits to flow through instead of just one? Thanks for your time, Tracy

Tracy – Mandrel bends shouldn’t effect flow too much, as fluids “roll” along the surface of the pipe they’re in. As long as that surface remains smooth, bends don’t have a significant effect…so I’d stick with the suggested sizes.

Crush bent pipe, however, can flow much worse than mandrel bent pipe – as much as 20% according to some things I’ve read. While you could go with bigger pipes to compensate, it’s better to go with mandrel bending.

As for cross pipes (x-pipes, h-pipes, etc.) they’re useful on V6’s for increasing the lower frequency sounds, and some say they work quite well on smaller V8’s from a performance standpoint. However, they have almost no effect on exhaust flow, so my guess is that most cars don’t need them.

David – Any of the popular systems will work, only you might think about going with a single side exit rather than a dual, as they tend to produce a little more usable torque (sometimes, depends on the system).

Whatever you do, make sure you buy a system that is tuned to your truck and offers dyno testing as proof.

Adrian – Dual 2″ or 2.25″ pipes all the way back will be plenty. Additionally, if you go with 2.5″ or 3″ duals after the cats, you may find that you lose a bit of power, as the exhaust gases will “backfill” that extra pipe diameter.

Or not – just depends.

I’m also thinking that you should dyno-test before you mount a system, as these accessories don’t always bring the promised power on an older engine.

Gday, interesting read, but 1 thing I did not see, tho i never read the whole comment section, is distance.

A 400hp mini minor compared to a 400hp cadi would require a much different size pipe, yet you have not touched upon this.
Are you just talking larger American size vehicles, or just a general all round sort of set up.

Im a diesel man in reality (boats) and our exhausts are sized not so much by power, but by distance from engine to outlet or tip.

David – The tubing diameter recommendations are based on gasoline vehicle implementations, where it’s understood that the system must be long enough to convey the exhaust gases from the front of the vehicle to the rear. Thus, system length is really not important (once it gets longer than 4′, it doesn’t make a difference).

Additionally, motor displacement doesn’t really matter either. Most engines burn about the same amount of gas to generate the same amount of horsepower, which means the volume and temperate of exhaust gases on a 400hp 4.0L are roughly the same as a 400hp 6.8L.

Of course, having said all of this, there’s value in calculating things exactly…which is why we say the chart is a shortcut.

Gday Jason, thanks for the reply.
The analogy between the two cars was more in that one will have an exhaust pipe as long as your forearm, the other a mile long.

One little thing tho, a 400hp big block will use a hell of a lot more fuel than a very modern 400hp fuel injected computer controlled car.

Im not pickig at all, just trying to work out the best for my toy, there are so many different aspects to think of, and some, (proven) go against every thing that seems rational.

In my mind, I see the very lowest back pressure as being the best, well designed will cause a vacume during cam overlap, and so gain best performance with a full charge of clean fresh air, any form of back pressure will negate this. Im having a hard time following the accepted norm, that a smaller pipe, so restricted, makes for better bottom end torque.

I see individual, tuned length pipes as being by far the best, (zoomi pipes) but sent to the back of the car, way over the top expense, and fitting would be a logistical nightmare, but if do-able, surely the best. IF you could tune these so that a pulse was leaving the tip as the engine was lifting the exhaust valve, perfect.
Understanding that this would mean a small rev range of perfection.

First, a note: You’re 100% correct that older and less efficient engines will push out more exhaust per HP than newer engines. However, in my experience, it’s not significant.

Second, the reason smaller diameters work best at lower RPMs has to do with exhaust gas cooling. If you dump hot exhaust into a 2″ tube, it’s not going to cool as quickly as it would if you dump it into a 3″ tube. Cooler exhaust is more dense (and therefore heavier), which means an over-sized tube at low RPMs creates pressure.

The perfect exhaust system would vary tubing size with RPM…growing from a 1.5″ tube at or near idle to a 4″ tube at WOT. Since no one has come up with a good way to create this sort of system, we’re stuck having to choose one size.

Therefore, you go with something a little small if you want low-end performance, and something a little big if you want high-end. Make sense?

Jason, Actually I think it does.Thanks for taking the time to help me understand exhaust a little. Sam

Mitch

Jul 11 2013

So i never got a response on my question about my 4cyl Hilux Diesel. I have ruled out the Cone filter idea due to the amount of dust in this region but are there any benefits to be gained from Straight pipe or highflow exhaust replacing the huge factory muffler. Sound, performance, MPG?

Great stuff here, need some advice. I have a 86 Chevy K10, 4×4, engine is a early 90s 350. Engine is only slightly modified. Looking for the most performance, HP, Tourqe! From reading I’m seeing I should be looking at maybe 2″ pipe or pipes? Not putting in a cat just pipe and muffler or mufflers. So question is 2″ or slightly larger and dual pipes and mufflers or go into a single muffler? Looking for the tourqe performance. Also what muffler do you recommend? Not concerned with it being to loud.Thanks in advance!

This is a great write up I would like to pick your brain though. I have a 402 with kooks headers 1 7/8 primary’s to 3 in collectors then my y pipe goes into a single 3 in pipe back over my Rearend to the muffler. I just SC the car and its putting down 792 to the wheels at 6800 rpm. Should I go to a 5 in mid pipe when the two 3 in pipes Y together then just take it to a cutout? Have no room for duals and can’t make it over Rearend with the 5 in

Hi.. I have a 2004 pontiac Vibe with a 1.8L 4 cylinder pushing out 123 hp.. I currently have 2 1/4 pipes from the cat back and a magnaflow muffler, with that current set up am I losing any power? What would be the best pipe diameter for my car with only 123 hp?

Garret – Removing that cats might effect performance, mostly because the exhaust manifold is designed to accommodate them. If you swap out the stock manifold for a header and remove the cats, you might see a small gain – 5% seems like the upper limit (6hp, give or take).

This is why I say that removing the cats is a waste of funds: Contrary to popular belief, modern catalytic converters aren’t restrictive. They flow pretty freely, in fact, and unless you supercharge or turbocharge your vehicle, there’s very little reason to mess with them.

I have a 2000 Chevy silverado 5.3 v8 all stock. I have true dual striaghts 2 1/2 pipe an 5 inch tips with no mufflers an cats an it’s the loudest truck so far. I wanted to make it as loud as possible any suggestions in pipe size or secrets ?

hi there Jason
I have a Volvo s60 t5(250bhp) that has factory 2.5″ single piping.. I have removed the centre box(22″ long) and replaced it with a jetex straight pipe now this might sound dumb im stuck with the rear box
can I reduce the size of the factory piping to say 2″ and if I do will it have any effects on the performance seeing as I have removed the centre box…????
the original box is over 28″ long and the replacement I have been looking at is 16″ (I will also be using mandrel bent tubing)
I don’t really drive the car hard I just wanted to let the 5 cylinder turbo roar a little better
big thanks from a confused scots man

hi jason
I have a 2000 Chevy silverado 5.3 v8 all stock. I have true dual striaghts 2 1/2 pipe an 5 inch tips with no mufflers an cats an it’s the loudest truck so far. I wanted to make it as loud as possible any suggestions in pipe size or secrets ?

Hi Jason,
I have 355sbc.It has about 400fwhp.Exhaust is SLP tri-y’s(1 5/8 primaries to single 3″ collector.Rest exhaust is single 3″ pipe to single dynomax dual outlet muffler.Do you think is exhaust on small side or not?

Jari – As always, the best way to answer your question is with testing. However, a single 3″ pipe is likely just fine for normal street driving.

If you’re trying to maximize your 1/4 mile time, I’d test adding a bigger (3.25) section of tubing between the collector and muffler. It will probably reduce performance off the line but improve flow at higher RPMs. But again, if we’re talking about a street car, I wouldn’t give it another thought.

I don’t know if you can help me but heres my question. I have a suzuki hayabusa. It came with duels from factory but now has a single exhaust.I’m trying to get a descent sounding shorty muffler for it, but dont want to hurt the bike in anyway. The bike has about 158 hp and the header pipe size is 2 1/4 in. I’ve been looking at a Coffman exhaust but they only come as pairs. I was wondering if I bought the pair but only used one would it be safe for the bike,also what might be the limition that I need to know so I can address them with the company? Thanks Sam

Jason, At some point before I bought the bike someone changed it over to a single exhaust header. When I got it,it had a yokoshima single exhaust . I just put on a 300 tire kit with a 12in stretched swingarm. A standard exhaust can not be used now because the swingarm is in the way and it can not be mounted as it was, so I need a shorty exhaust. I’m just trying to find something that won’t hurt the bike. If I understand things,as long as the muffler has a connecting pipe the same size or a little bigger than the header pipeit will be ok. Is that right?

Sam – A good rule of thumb is that an exhaust system can’t hurt your bike at all mechanically, and that going with whatever tubing diameter you have now won’t change things much.

I’d say that you want to make sure whatever muffler you buy is designed for a bike like yours with a single exit…most muffler manufacturers can recommend a couple of options (either on their website or by calling their 1-800 number).

Im in same situation…but i have stock header with duel outlet and i caped one of outlets off, so now only one is used with an stubby can i bought. Will there be any issues running like this till i can afford a single sided header? or is there no need can i just run as is and just do PowerCommander tune?

Yuki

Oct 19 2013

Hey Jason, I recently bought a resonator and a muffler without doing much research on diameters. The resonator was 2.25 in and the muffler was 2.5 in what effect would that have on my car if I welded it on there with the stock piping being 2in? Thanks!

Hello Jason,
Back again, we have discussed my regal and now its time for the toyota pickup. Im setting a 6.0 ls1 bored and stroked to 409, square port 2.06 heads and supercharged. Low boost around 600hp. According to ur chart dual 3″ is good for just over 600. Not quite sure what its gonna b putting out exactly yet, but im looking forward to that 650+ mark. Dual 3″ should b enough Right, around 7,500 rpm is the range im looking at. According to the mathematics i should b ok, mayb a little under sized for the top end being forced induction. But i dont want it too loud. Maybe go a little bigger on the pipe to run a quiter muffler to make up for loss of flow?

Frank – My only thought is that you supercharger will hide any potential problems with exhaust gas restriction at the lowest RPMs…going to be very hard to notice the difference between a 3″, 3.25″, and 3.5″ tube (at least in my opinion). As always, testing both a 3″ and 3.5″ setup would be ideal, but I don’t know how feasible that is.

If you’re looking for a shot from the hip from me, I’d say buy whatever size you can get that matches the muffler you want. 🙂

Currently have a 2008 Pontiac G8 GT with the 6.0L Bought the car with headers w/o cats. I had a exhaust shop in town to take out the mid muffler and added a x-pipe (the butcher it all up) Had the magnaflow mufflers taken off and add flowmaster 40 series, I know that most people wont look under the car, it looks like crap. I was wondering if i should keep it (i think its 2.5″) or go up to 3″ exhaust pipe. Currently exhaust is a true dual setup. Hoping for a different cam and such in the future.

I’m currently building a 383 for my truck and I have a few questions. Idle to 5000 rpm motor and I’m anticipating the 350 HP range and 450+ tq. I plan on using 1 1/2″ primary port matched customized headers (mid length) and dual 2 1/4″ mandrel bent exhaust with magna flow center/offset straight thru mufflers (I want plenty of low and midrange power but I don’t want to fall off up top).
1) Is 2 1/4″ gonna be big enough in towing/hauling situations?
2) Do you see any benefit in a merge style collector (2″ outlet transitioning back to 2 1/4″ or 2 1/2″ final outlet? I’ve been told they increase low end torque.
3) I planned on installing an H-pipe behind the collectors. It is my understanding that they help balance the uneven pulses in the v8 firing order and also give a deeper, throatier sound to your exhaust but I get the impression from reading your responses that you’re not very supportive of a crossover on v8 dual exhaust. Can you expand on this?

1) Probably so…the times you need power are lower RPMs.
2) Yes. I’ve seem some data to suggest these 4-2-1 collectors facilitate scavenging at lower RPMs (depending on the length of each tube).
3) I’ve never been a big fan of h-pipes on V8s.

First, the pressure waves are coming at the same time from both sides of the motor on a V8, so the sound is basically balanced already. There’s probably a slight diff. in the distance each wave travels, but it’s got to be miniscule in such a short span of tubing.

Second, the h-pipe is only going to have meaningful airflow if the pressure on each side of the pipe is different. Since the pressure waves are basically coming down each side simultaneously, there’s little to no flow…and thus few benefits in terms of sound.

BMW 3.0 straight 6 (S50) with about 270 crank HP at 7000 RPM. I currently have stock exhaust manifolds and OEM dual cat/pipe setup with a gutted muffler. I will be installing a factory header and would like to switch to a single high flow cat and pipe setup to a single Borla muffler. Would cat back 2.5″ pipe be suitable?

I am trying to figure out what size of exhaust pipe to run on my 3.4 6cyl. it is stock out of a 1995 Firebird. The stock header pipe is 3″ To me that’s a little big.
It comes together into a single pipe. I am not running a cat. and am wanting to go with a 40 series flowmaster muffler.
Would I be best to go with a 2.25 pipe into the muffler and out as well?

Hoss – The chart is pretty clear…you look up the horsepower of your engine (which, btw, I have no idea what you’re running) and then the recommended size is shown. If you’ve got a 6 cylinder, a 3″ is probably too big and a 2.25″ muffler is probably OK. If you’ve got a V8 (or you’ve hopped up your V6 a lot), than 3″ might be OK and 2.25 might be too small.

Hi Michael,I’m running a 572ci Chev producing 650hp and run twin 2.5 inch pipes, unless your racing yours using twin 2.5 would be ideal as you won’t be able to push your car on the street beyond that pipe size capability anyway and going bigger will cost you low end torque not to mention the cabin noise problem and if you do drag it you can just remove exhaust from collectors back anyway.

Hi Michael,I’m running 650 HP through a twin 2.5 inch system and would suggest you do the same unless its a drag car but then you can just remove exhaust from the collectors back,you won’t be able to push your car on the street beyond the capacity of a system that size and will have optimal low end torque

My first idea was to make the middle section 2.25″ and the rear section 2″ so the velocity in the exhaust will be good. (I heard more often that a smaller rear diameter will be good for that purpose,)
Problem is that over here the 2.25″ isn’t common, so it’ll be either a 2″ or a 2.5″. I think 2.5″ is too much while it’s a daily car and i don;t want too much noise. Besides that i’d like to keep some torque available for the daily rides.

onnaj – I like your ideas…stock exhaust tubing is generally just fine unless you’ve really tweaked the output of the motor. Since you’re rated at about the same HP as the factory setup, I’d say factory spec sizing is best.

Additionally, I’d go with 2″ instead of 2.5″ in this case. 2.5″ is big for a small 4-cylinder. 🙂

If you look at the chart, 180-190 CFM corresponds to a 1 and 5/8ths diameter. This is close to 1.5″. If you’re trying to maximize top-end production, bigger tubing (2″) will do it. If you’re trying to build up the low end, 1.5″ is fine.

However, you also want to make sure the header tubing is larger than the exhaust outlets on the head. There should be a short “cliff” or “step” between the head outlet and the header inlet. This acts as a barrier against exhaust gases flowing back into the head.

Thanks for the quick and detailed reply. No doubts any more that i’m going for 2″ but use the stock 4AGE 20v 2.25″ downpipe!

Joe

Feb 5 2014

First off thank you for this information.

My car is a 2009 Dodge Challenger R/T. The engine is a 5.7L V8 but is supercharged, cammed, and has worked heads.

My exhaust appears to have several changes in sizing. I am running 1.75″ JBA long tube headers going into JBA catless mids at 2.5″. They then go into my DynoMax VT catback with a 2.5″ in then 3″ out x-pipe. The remainder of the exhaust is 3″ all the way back until where the tips clamp on. At that point the pipe is reduced down to 2.75.

I am looking to buy a set of catted mid pipes from JBA. They have a set that are 3″ instead of 2.5″. I can also get another X-Pipe from DynoMax that has a 2.75″ in and 3″ out.

So should I buy the 3″ catted mids as I exceed the horsepower of 2.5″ currently. Also, does buying an X-pipe that is 2.75″ in versus my current X-pipe having 2.5″ in and both are 3″ out or basically a .25″ increase on the in side warrant the purchase of another X-pipe? Does an exhaust system come down to it’s lowest denominator? Meaning the catless mids are 2.5″ mating up to a X-pipe @ 2.5″ in. So does the fact that the X-pies is 3″ out and 3″ rest of the way matter? Is it ultimately a 2.5″ system? Even if I bump my catted mids up to 3″ and it then necks down to 2.5″ or 2.75″ make the rest of the systems diameter a moot point?

Amazing how I can be so long winded over ultimately a .25″ increase in size at only one junction of the exhaust system. Devil is in the details though.

Joe – First, I wouldn’t worry about the x-pipe. On a V8, that pipe is pretty much meaningless…each side of the system is flowing at nearly the same rate at any given point in the RPM curve. There’s little to no reason to balance the tubes on each side of the system.

As for replacing the 2.5″ mid pipes with a set of 3″ mid pipes, I’d say you’re one of the few people who should seriously consider it. You’re running a heavily modified high horsepower V8. You may have a flow restriction at higher RPMs if you’re pushing 700hp.

If you’re closer to 500hp, I’d say you should stay with what you have.

Question of a newbie 🙂
i just had my exhaust pipes replaced yesterday and I felt that i just rob some hp to my engine. I’m not yet sure if I got the wrong feeling, maybe because of the noise or the vibration or whatever but I think the response and the peak power of the engine is not as powerful compare to the stock exhaust.

I have a 1995 Civic Eg D15 engine
1.5L 130hp (stock)

this is what I did:
directly from the stock headers, I replaced the stock 1.75″ pipes, 2 stock resonators and the muffler to a customized 2″ inlet, 2″ outlet, 24″ muffler

the sound is great (deep and bassy) but I want to know for sure if I gained a little power or just the same as stock or unfortunately ruined my engine performance.

please enlighten me, is it an improper customization? or did I miss the proper calculation? or do I also have to change my headers first to match the muffler?

my thought is replacing a larger diameter/aftermarket headers, pipe, and deleting some restrictions will give the exhaust air more room to flow. why does it still need a proper size/diameter while logically the larger it goes the better air flow?

your reply will be really helpful to a newbie like me.
thanks in advance for your advice!

Jun – It’s not just about removing restrictions – it’s also about making sure exhaust velocity is high enough to facilitate scavenging at lower RPMs. The only thing you mention that concerns me is replacing the connection between the stock manifold and the after-market muffler. The stock exhaust between the head and the end of the catalytic converter is usually sized perfectly for your engine. If you replace that tubing with something larger (and omit the catalytic converter in the process), you can see big changes in performance (usually in the wrong direction).

What about replacing the stock manifold with a header? You’ve gone this far, why not go a little further? There are lots of headers out there, some of which are designed to work with larger tubing.

Hi Jason, I really appreciate your time responding to a begginer’s question.

Well you just enlightened me with your answer. I was almost thinking the same logic behind what happend to my car’s performance. Its basically a missed match between stock manifold and a customized muffler. (Do it once, do it right) i should have considered replacing the whole exhaust system with aftermarket parts if im after the performance than the way it will sound.

However, Im now willing to go further… Hahaha
Can you help me again doing the right choice this time?
I need to know the perfect headers for an all stock D15 vtec engine (P08 head, intake and box) (20 camloabs) (130hp) the options in the market is a 4-2-1, 4-1, tri Y and side exit headers. Which one will be the most effective considering that my engine is stock.
And how about the piping?
I really like the sound of a straight pipe, is it also applicable to my engine?
Future/next upgrade will be cam gear and box tuning.
What is your advice by also considering the future upgrades that i can do with the engine?

I hope to get an answer from you before I commit the same mistake again hahaha
Thanks for your reply, i really appreciate that Im having a credible answer from the expert.
God bless!

Jun – Most of the exhaust systems for the Civic are designed for heavily modified motors…if you put a header designed for a turbocharged engine on a regular engine, you’ll probably be disappointed. My advice is to a) only consider header manufacturers that provide dyno data/charts and b) make sure you know what your plan is. If you’re saving up for a turbo kit, you might want to wait to buy the headers until then.

If, on the other hand, you’re just going to do a few minor upgrades, I’d look for a header that shows improvement on a stock engine. It doesn’t really matter what the design is either – the key is the length of the section between the head and the collector.

First let say I’ve really enjoyed reading the science behind the equation. .I would appreciate your thoughts on what I would like to do ..I have a 2000 sts cadillac with a few upgrades for hp running approximate 330 hp and stock exhaust… what I am thinking is custom made headers by Carroll customs and after the cat …remove the stock 3in pipe and mufflers to y off the cat meaning from 3″to dual 2 1/4″ pipe and where the exhaust divides to the mufflers add a x pipe to pull exhaust then go to dual magnaflow 11225…I’m hoping this will not be to much and loose power …I’m looking for a more deep throated sound without the tickets as was mentioned in your article. ..lol

Dean – I’m not 100% certain on the exact arrangement, but it sounds like you’re mounting a dual system to a V8, with headers and everything. First I would advise that you ask to see a ‘before and after’ dyno chart for the headers. Sometimes headers take power from the bottom end to add power to the top…it raises peak HP, but it makes your car less fun on the street. Second, I would say that V8s don’t really need h or x-pipes. They’re essentially balanced, so adding a tube connecting each side isn’t really necessary. Three, the mufflers will do more to dictate the sound level than anything else you buy. Make sure you’re OK with those Magnaflows, as they’ll probably be loud for a Cadillac. 🙂

Hello,
I currently have a 02 Nissan Xterra Stock Supercharged (for now) and am looking to swap out the exhaust. I would like to eventually swap out for the smaller 2.35 pulley instead of the 2.64 on there now. Also stock is only about 210 hp, I have an upgraded CAI. Headers would be a consideration in the future as well. There are currently 4 cats on it. 2 primary and 2 secondary. I would like to buy the Exhaust pipe to replace the secondary cats as they are sold legally for a 00 to 01 xterra. Looking into the the exhaust diameter, would you recommend the 2.25 or bump up for the 2.5? I would be replacing the very restrictive y-pipe that is currently on there.

Would there be a problem if i went 2.5 into a 3 inch collector back into 2.5 duals? I would be doing the exhaust custom i understand just wondering if that would kink up the exhaust too much. Right now my y pipe is perpendicular and very impeding to exhaust flow. I would pretty much run the pipe as a dual set up with a collector pipe. I appreciate your feedback!

You are correct. For some unknown reason, Nissan put four cats on some of the xterra/frontier. I would love to rid of all of them, but as I have read from your earlier posts, they shouldn’t be too constricting compared to hiflow as they are pretty good compared to days of old. But, I would be doing it possibly from the first set of cats and getting rid of the secondary cats, as I have found that Walker makes Federal legal pipes. so i would get those and finish out the exhaust as mentioned. I just one would like the sound to be ddecent, but two increase the flow for future mods, as mentioned. Thank you Jason its been great help so far!

Ed

Mar 2 2014

Hello,
I have a 1999 Ford F150 with a 4.2 v6. The stock HP is at 205. The previous owner threw in a K&N air filter and a 2.5 inch cat back dual exhaust. It is stock from the manifold through all of the cats,then to one stock 2.5 inch y pipe, then to one 2.5 inch pipe to a hi-flow muffler and splits to to end pipes measuring 2.5 inch throughout. Since it is all rusting out, My idea is to go with a direct dual exhaust throughout the entire system after the cats on each side of the manifolds. Your page says I should be at 1 3/4 inch throughout for a 217 Max HP. Would you recommend both pipes to share one muffler and exit out dual or go with a muffler on each pipe of its own?
Thanks for your help.
Ed

Hi, I did some more research and learner the stock set up for my F150 was a v6 dual manifold feed into one pipe and muffler all through a 2.5 inch tube. This all corresponds with your chart above given the fact that the stock HP is 205 ponies. Reading some more feeds on your site tells me you don’t recommend H or X pipes for your typical HP recipes. Doing the math and my research brings me to a calculation if 1.58 inches for a dual pipe set up. Now my question to you is, since I will be going with a dual 1.75 inch set up, (1 3/4 is easier to find parts for) would you recommend bringing the two pipes into one muffler then two pipes out (since the pipes are slightly larger than recommended) or going with a muffler on each pipe? Any help would be greatly appreciated.
Thanks,
Ed
PS
I thought you would appreciate me doing some homework on my own LOL

Jason, I’m still tossed on a true dual with a muffler on each pipe or dual in dual out muffler. Everywhere I have read I get mixed reviews. Some say true some say DI/DO. In your honest opinion,(given your knowledge) of the two, (a) What would be best for performance? (b) What would give me the best sound? What direction would you choose?

Jason, my apologies for running you through the department of redundancy department. LOL! When I read the thread I did so on my smart phone an the replies were reversed so I only saw your second reply. Just goes to show modern technology at it’s best. Ha ha! Great site, a ton of info here! Thanks again. DI/DO way to go.

Sid – Those numbers sound awfully high to me, considering a 5.0L V8 only takes in 440CFM worth of air.

By my calculations, a 600cc motor at 8,000RPM is going to suck in 85CFM (I know, I’m mixing units). Even with fuel, I doubt that engine produces more than 100CFM of exhaust…and that’s at or near WOT (I’m assuming a redline around 9k?)

Another thing to remember is that the chart above isn’t really relevant to race scenarios…I’d suggest cracking a textbook, talking to another race team, or getting with the prof. on this one.

OR, even better, put whatever you think is right on the motor, test it, and then compare. That’s the beauty of being in a university setting – you’re free to think “outside the box”.

In the post above it doesnt mention how we can determine the actual diameter of the muffler with the CFM except from the table. In this case we could manufacture so stock diameters are not really needed if a specific diameter can be calcualted but I am unsure of the next steps?? could you please assist me on what the next steps are??

Next step: Assuming a pipe will flow 115CFM per square inch of area, back into your pipe diameter.

Then, find the closes off-the-shelf pipe size. Since your motor is all top end, I’d hedge towards the larger size of pipe.

In other words, if your calcs indicate a 3.65 inch diameter tube is needed, go with 3.75 or 4. This is OK on a high reving engine that makes all power on the top-end (at least assuming the engine spends most of its’ time at high RPMs).

The area of a circle is Pi * the radius of the circle squared. You know that exhaust tube flows about 115 CFM per square inch, so you take your CFM (547), divide by 115 to get an area, and then back into a diameter.

Just one last question, this outer diameter is it irrelevant to what type of muffler it is?? as in a straight through, chambered or turbo? all could have the same outer diameter for the calculated CFM.

hey jason,
for some reason my comment didn’t post on this thread yesterday. I have a 2013 tundra completely stock. They make about 381 engine horsepower. I looked in to getting dual exhaust and the shop recommended a cat back dual in / dual out magnaflow. I was wondering if it would be better to actually spend a little more money and use two mufflers instead of one? The stock tubing is about 2.75in and the exhaust shop uses 2.5 inch. I noticed above that you said a 400 HP engine only needs 2.25-2.5 in tubing but I was wondering if going to a single dual in/ dual out muffler would be a good idea. Or should I get two single in single out mufflers? The shop I went to said it would make no difference. Thanks in advance, -Matt

Jason, Thanks for the quick response. I guess the second part of my question was is 2.5in tubing too small to be considered properly sized? Like my earlier comment said, I found out stock tundra tubes are 2.75in. How can I ensure that this system is not too small or too large in terms of tubes?

I just happen to know in this situation that the exhaust system on the Tundra was very carefully designed. I would absolutely make sure that the tubing coming into the muffler didn’t change in diameter.

However, once you get out of the muffler, the tubing size isn’t too critical.

Jason..
I have a 1998 Chevy Silverado with a 5.7liter I wan yo replace the stock exhaust with another set up not quite sure what’s the best size for efficiency the truck is stock but I know I need a new system due to melted cats I would like yo leave room for performance because I’m in school at the moment so I don’t want to have to re do my exhaust again I was thinking 2 3/4 any suggestions?? Thanks

Jon – My best suggestion is to buy a tuned cat-back system designed specifically for your vehicle. They offer the best combination of performance and sound quality, and they’re relatively affordable ($600-$800). If you don’t have the money to do a full cat-back, than I’d just replace the mufflers and leave the rest alone. Increasing tube diameter isn’t usually impactful on stock trucks.

So, going from long tube headers with a 3″ collector to about 24″of collector length to a 2.5″ reducer to terminate the collector length effect, then going to a single 3.5″. On a built dodge 5.9 at 9.6 comp. It has a bit of a lag at 1500. Set up to shift at 5500.
This is what I am considering. Any feedback?
Thanks
Ron

Ron – Does the header manufacturer have a recommendation? What you’ve suggested seems reasonable, but I’m wondering about the value of a reducer that’s 2 feet down the line. If the collector is 3″, and it’s designed specifically for your engine, than 3″ is probably the right tubing size.

If the headers with a 3″ collector are not designed for your engine (and honestly that sounds very big), you’re probably not going to like the final result. Over-sized headers usually zap power.

Jason, Yes the headers are for the rig. 1 ¾ prime tube with 3” collector, with a 3” Y pipe going to a single 3” I have a Hughes airgap intake as well. Sound is a bit of an issue as well as power at around 1500. I have done some research on this topic and it would seem like collector length is a major factor in creating balance between the two sides of the motor, and moving the power down to where it is needed. 24” seems to be the target for my RPM range of a 5500 shift. As it is now I feel like it is unbalanced with the driver side twice as long to make the trip over to the other side.

Ron – Unless we’re talking about a diesel 5.9L, those headers sound like they’re for a race motor. They’re too large for a street motor, at least if you want to make power at lower RPMs.

When you have headers that are that massive, they tend to “back up” at lower RPMs. The engine is probably producing 80% of its’ torque at 1500RPM, yet you’re noticing a lag. My guess is that the exhaust velocity in your headers is too low at these lower RPMs.

Now, if you’re trying to maximize your quarter mile time, or if you’re running your vehicle around a track, this type of header design is A-OK, as the engine spends most of it’s time at higher RPMs. But if you’re putting headers like this on a pickup you drive to and from work every day, you’re going to notice power problems.

In short, I don’t think collector length is your problem, at least at 1500RPM. I think the problem is that your exhaust velocities are too low at low RPMs, which means you’re not getting the scavenging you want.

Jason, I have an Old’s 455ci auto, 320Hp 460lb-ft with the original 2into1. The left pipe 2″ crosses under the sump to the right manifold and a 2 1/4″ pipe runs from there to the muffler then a 2 1/2″ pipe to the rear. Its too quiet, like silent, so I was thinking a true 2into1 to free up some ponies and let it sound more aggressive. My plan is a 2 1/4″ pipe from both manifolds back say 36″, then both into a 2 1/2″ for about 24″ into a free flow muffler. From there a 3″ pipe the rest of the way mandrel bends over the diff and out the back.
I think this will provide good scavenging without losing bottom end torque and make it sound more beefy. Useful rev range and power is for street driver, idle to about 4 grand.
What do you think, am I close with this? Any suggestions. Cheers, Dave.

David – Sizing sounds right to me. The only tip I have is that you want to design the exhaust to go with whatever manifold or headers you’re going to install later. If you’re going with some performance headers down the road, I’d recommend building things with that in mind.

Hi Jason
Firstly, great info to simplify things for us laypersons…I know you are busy with all the posts so I’ll keep this as clear as possible.
I live in the UK and have a 2006 1596cc NA engine Ford Focus…stock power is 100bhp with 1.75″ tubing, centre resonator and chambered rear muffler….and now my exhaust needs changing. The only full SS cat-back system in the UK is (Piper Exhausts) is 2.25″…which according to the chart is a bit too big…However I can get a custom one made to my sizing…since I’m planning on upgrading the intake, ignition, replace exhaust and get a re-map at the end…it may take the car to 115-120bhp…so my questions are these:

1) Do I stick with 1.75″ or go 2″ with tubing as with the extra power its kind of in between sizes (according to chart) but nearer the 1.75″?
2) I used to work with office and industrial air-con systems and there the ductwork used reduce in cross sectional area the further it got from the fan….so an idea someone above suggested how about 2″ to the resonator (about half-way) and 1.75″ to the rear silencer in the interests of flow velocity? or stick with one of the sizes in Q1?

1. I usually go smaller when it’s between sizes, especially on smaller displacement enignes.
2. Flow velocity is also dependent upon the temperature of the exhaust gases. If the exhaust gases were staying at the same temperature as they traveled thru the system, necking down a section of tubing might be a good idea. However, they gases are changing temperature as they move, and – typically – necking down the tubing has minimal effect on velocity.

The best way to keep velocities up is to keep the tubing just barely big enough to do the job. Hence, my suggestion to go with a 1.75″ instead of a 2″ if you’re between sizes.

I had a quick question regarding this topic that I was hoping one of you pros can help me out with:

I recently installed a new Cat. Converter to my 2000 Chevy Cav. Z24. Im in California so I didn’t want to throw down a good wad of cash to only end up having problems when it came time to get it smoged. I went with a 50 state legal direct fit Magnaflow cat instead of getting a way cheaper but more likely to give me problems Universal cat. so this Cat came with the flex pipe/down pipe, honeycomb Cat., and the pipe at the outlet of the Cat which houses the O2 sensor and the flanges at each end of the unit for easy no weld bolt on installation. the problem im having now is the rest exhaust system(resonator pipe, muffler). initially I was planning on purchasing a obx cat-back system they offer which includes the new N1 style muffler already welded and ready for install. the mechanic who helped me install the Cat Converter did a quick check of the old resonator pipe and told me it was still good so that made me lean towards only purchasing a performance muffler now… only thing is that my exhaust systems pipes are 2″ inlet and outlets. the smallest inlet on a good (50$)muffler has been 2.25″. is this common and there is there a way that a professional makes it work? and might it effect my cars performance? what do you recommend? im open for going with the obx cat back if that would give my cars performance a substantial boost in highs and lows, or would getting a new muffler give me about the same boost in performance?

I have a 2006 ford fusion V6 with a Steeda cold air intake and soon a tune with Steeda custom tunes and a Steeda throttle body spacer. It’s stock 221 hp but with all that it’s got around 280-300 and don’t know what size piping to get. The flow master cat back is like 2 1/2 but I’m having a buddy’s step dad do it. They work on drag cars a lot and was gonna have a custom system put in to get some deeper idle tones and a bit of a bark when I step on it. I don’t want to go to big because the back pressure. But need to know a good size to up it too. The pipe looks really small just haven’t had time to measure or anything. I had the resonator deleted off of the car which have it a deep tone on idle but other then that nothing. Help?

It’s single all the way back to I’m pretty sure right before the axle then it y pipes into two But I don’t have money for te Steeda one. Plus I was looking at flownaster or Magnaflow and it’s like 2 1/2 or 2 1/4 which is what I’m thinking about matching. With some flow master super 40’s

can anyone tell me how much will be the average size or specification of the motorbikes silencer? because i am working on the project where i am designing one. but it a air preheater which will connet to the exhaust pipe. so ideally i want the specification for air preheater(heat exchanger) for a bike which will look like silencer.

You guys are about performance, but I need guidance about not damaging the engine or clogging up the cat.
I have 2006 Ford Freestyle with a 3L 6 cyl that had the only muffler available in a tiny town 1,000 miles from home put on (Not the right one!). It is about 4″ shorter, and they had to put on a 45 elbow that necks down to 2″. The muffler inlet and the pipe from the front both are 2.25″. The outlet is two 1 7/8 pipes so together they have way more area than the inlet pipes.
My concern is not HP, it is damage or long term harm to the engine, or soot collecting the the cat. As you can tell, I have no experience, I just read that a restricted flow is not good, but I have no way to gauge if this is a non problem, small problem, or big problem. I want to baby the engine because I need this vehicle to last. Do I need to replace it with the right muffler or am I OK?

The good news is that a muffler that’s actually designed for your vehicle can be purchased after-market for $75 (give or take), and most muffler shops will install it for about the same. I’d guess that the $150 you’ll spend buying the right muffler will save you some gas money every time you fill up too.

I have a question I have an audi 2001 s4 it makes 500hp at the crank, my question is how big of dual exhaust do I need ? would a 3″ downpipe to a dual 2.5″ ehaust be better than a 3″ downpipe reduced to 2.5″ then bolted to a 2.5″ dual exhaust be better? to me i think they basically are the same because either way its being reduced to 2.5 inches but am I wrong? is this big enough for my horsepower? oh and the car is twin turbo and not remotely stock it is rs6 conversion.

Dom – When we’re talking about forced induction, a lot of the concerns about exhaust cooling and “stopping up” an over-sized exhaust pipe go away. Not only are exhaust gas temps generally higher on a vehicle with a turbo or supercharger, but scavenging is less important.

Basically, if you’ve got a turbo or supercharger, you can go bigger than you would otherwise go. I’d go with the 3″ downpipe to the muffler, then whatever you want from there.

Yes agreed and thank you for the response. The 2 down pipes is full 3″ then into a 2.5 ” full dual exhaust should I go with full dual 3″ or does a 3″ tapered to 2.5 downpipes to a true 2.5 dual exhaust the same as tapering from full 3″ downpipes to a 2.5 exhaust?

Dom – Going with 3″ all the way to the tailpipe seems aggressive to me – I’m not sure you’d suffer any power loss, but you might have a little more punch off the line if you go with a 2.5″ exhaust from the muffler back.

As for the downpipes, I’m a fan of bigger on this sort of application…only the *best* way to know is to test both the 2.5″ and 3″ downpipes and see which does better.

Hey guys, wonder if you can help me, I have a measely little 1.5 Suzuki Swift, and I’m looking to change the exhaust, it makes 75whp haha and redlines at 6200 rpm, the stock exhaust size is 2″ from what I can see, would there be any benefit going to 2.25″, or would sticking with a 2″ stainless system work better?

BMW 2014 X6 5.0L bi-turbo putting out 450BHP/480ftlbs, anyway – I swapped out the too-refined factory muffler (2 pipes from the engine to a single muffler) for a Meistershaft EV system (not cheap at all) which has a pair of independent mufflers per pipe (2 tips per side, 1 from each can).

Problem is that at low RPM (1000-1500 ish) I’m getting a “pulsing” sound some of the time. Once gas starts flowing the nice noises start, so my question is.. any ideas?

The system also has valves on 1 of the mufflers on each side that can close one of the tips – if I do that the pulsing is much more pronounced .. reminds of of how a V8 VW bug might sound.. not at all a nice V8 growl..

I’ve been wondering about X-tubes, H-tubes (before the mufflers) anything that might merge the gas flow into a more uniform flow..

Hey Jason, figured I’d give an update .. An exhaust shop created me a custom X-pipe installed between the resonators and the mufflers – it has completely fixed the problem, the sound is a nice even rolling growl and with the EVs closed the system is close to stock sounding.

my 93 chevy trucks 4.3 needs a new exhaust system it has stock everything 2.75 cat to 2.25 pipes. can i use a 2.5 muffler+tailpipe or duals without any loss in power or just keep it stock with a good flow muffler?

Jason Help if you can
I have a 93 Dakota 4×4 from my fathernlaw kept burning up transmissions ,Exhaust crossed within 1/4 inch of tranny pan bad design baked fluids in pans I now have cutoff the exhaust so drivers side comes straight back instesd of by pan and over to Y on passenger side will 2.25″ work to run it back and around tranny for dual out ok & I welded up the Y xtra Hole but the 2 in outta the manifold runs into 3 in at the Y with oxygen sensor that wires were cut off but 3in runs into a old cat burned up can I eliminate that cat and run 2.25″ straight back also or should I get a new cat and sensor & if I get the new cat will just runnin it on one side be ok ??/ got six kids Low budget doin myself need a little advice Guys Thanks for any Help, Bubba

Leroy – Aside from the fact that eliminating the cat could cause problems when its’ time to pass emissions, eliminating the sensors will probably cause the engine to run poorly. You can buy oxygen sensor simulators to try and “hide” the fact that the cat is missing, but it’s not a bulletproof solution.

My honest suggest is to try not to put much money in it. I personally owned a 92 Dakota, and it was by far the worst vehicle I ever had. 🙂

Leroy, I know Jason knows more than I do about exhaust but just thought I’d give you a real world experience from a previous 93 Dak owner. I bought a 93 Dakota brand new. Had the 5.2 with A518 trans. First off the crossover is not what is/was burning up your transmissions. I’ve been rebuilding torqueflite’s for nearly 33 yrs. and have seen many crossover pipes pass right by the trans. pan and they never burned up the trans. My guess is they are not being rebuilt correctly. So many rebuilders just yank stuff apart and slap new clutch plates in something and call it rebuilt without even checking any clearances or replacing bushings or steel plates. Some don’t even service the valve body. IMO they just “patch up” the trans, not rebuild it. That aside lets talk exhaust. When my Dak was about 5 yrs. old I decided I wanted to have dual exhaust on it and had the same concerns as you but I took all the factory exhaust off and had 2.25″ duals ran and installed a single exhaust bung in the right side pipe only and it ran just fine other than fuel mileage dropped slightly.

BTW: funny Jason’s Dak was so bad. In addition to using mine in everyday service I raced it a whole bunch. I’m sure I made at least 500 trips down the 1/4 mile drag strip. Wasn’t real fast but I did get it down into the 14.40’s. Sold it with a little over 90,000 miles on it with the original engine (never even took a valve cover off) and original trans with just a Trans-go shift improver kit and it still worked fantastic the day I sold it to a tree trimmer and he ran it until it had 130,xxx miles on it before the trans gave out. Other than general maintenance and 2 wiring issues and 1 blown heater hose it was a fantastic vehicle. Unfortunately yours has time (and probably a lot of miles) against it so I agree with Jason in not putting too much money in it. Good luck

I have a 1991 gmc Sierra with no cat or muffler and it feels a little more gutless than what it used to be. It’s set up with 3 inch piping all the way back to where the muffler was and then 2.25 the rest of the way. Is there any way or suggestions on what I could do to gain back power without putting my cat back on and muffler? Thanks

I recently built a carbed 383 stroker for my 94 chevy fullsize truck. I didn’t get a chance to put it on the dyno before I had to get the truck going but, by my best estimations and calculations it’s making around 410-420hp. I use it as a daily driver and for pulling a fairly heavy toy trailer on a lot of weekends. I had a built 4.3 v6 in it before this and I had dual 2″ exhaust ran from the manifolds to behind the rear tires which was plenty for that motor. While this works, I notice when I step out to pass someone going down the road it builds hp fast ans strong up to around 3800-4000rpms and then it seems like it really isn’t gaining anymore power. I’m looking at a 2 1/2″ mandrel bent header back system that I would end up building/installing myself and if I understand the chart right this should be a good size for my application correct? I plan on using Flowmaster’s deltaflow 40 series or their super 44 for the quiet down parts. BTW, have you had a chance to hear the difference between these two yet?

So I got a question for my 95 civic dx (I think 1.6L or .5 not sure at the moment) but I just installed a fairly cheap exhaust with headers, cat back and everything else but I broke a bolt on my cat converter cuz some dumb ass tacked all the bolts on the stock exhaust so I just have a test pipe til I fix the cat. The new exhaust is 2″ with a 4″ exhaust tip. I recently replaced the spark plugs and the only other upgrade I have is a spectra cool air intake.

So my questions:
1) Is the pipe too big for a 4 cylinder civic?
2) Since its aftermarket and more air flow, will the intake have more effect on hp? (With a 4 cyl I’m not expecting much but I’ll take wat I can get.)
3) Idk if it’s true but better overall performance? And maybe a little more fuel efficient?

Anything else u wanna add is greatly appreciated!
Thx for takin the time to read this!!

Nate – I’m not sure what you’re asking re: intake and #3, but i’ll say this: you’re not going to find a lot of power on a small 4cylinder with intake and exhaust. You’ll want to bolt a turbo onto that engine to get any real power, and you’ll want to pair the turbo with the exhaust system and intake.

If I were you, I’d save my pennies for a turbo kit and stop with all other upgrades. Unless you’re willing to strip down the motor and get a new cam, upgraded internals, etc. They you might be able to get some more power.

My ex worked at a muffler shop and a guy brought in his truck for a custom muffler. He brought home the original. I have talked to a couple people that have told me it’s worth money. My question is how do I figure out how much to ask and what it goes on? There are no numbers anywhere!?!?!?

I am bringing a 62 cutlass back on the road. It has a alum 215ci 4bbl with 10.25 compression which ran factory hp at 185bhp. A better cam, and carb, and balanced it looks like around 200hp at 5000rpm reving to 5500-6000. Nothing much but I want it to breath well out the back with dual exhausts. Your table looked like 1.75″ dual exhausts and I’ll try to fit a cross over in. Does that sound right?

Jason, thank you for the very informative article. I have a question, I have stock 454 out of a ’72 passenger car. It doesn’t have any smog equipment on it. It has the stock manifolds and a 650 Street Demon carb. I rebuilt the motor and left everything stock except the cam. I put a very mild cam that’s supposed to increase torque. I have this motor in a 58 Cadillac and all I do with it cruise. I wanted a super torque monster motor for my application. This motor will rarely see anything above 4000 RPM’s. I also have a 700R4 tranny and this thing cruises around 2200 RPM’s at 75 mph. I opted to put 2 inch straight pipe all the way to the bumper instead of 2.5 due to wanting to maximize the torque. I don’t really care about the horsepower. Question, is the 2 inch pipe appropriate for my application? I’ve read a lot of articles about 2.5 inch stuff going on big blocks but they’re more geared towards higher horsepower and performance. I just want to cruise and keep her at low RPM’s. I plan on eventually adding an EFI system but that’s going to be geared more towards economy and just over all running better. Once again, thank you for your time.

Problem found with most small motors, even gas (such as generator) is that the noise does not come from the exhaust. The noise is from the workings of the engine itself. Many “silenced” generators are enclosed in boxes with soundproof materials on the inside. You can see results of people trying to muffle small engines all over on youtube, and as far as I’ve seen, it’s all fruitless.

So I have a ’96 Ford F250 with the 7.5L 460. Being the fool I am, since there are 2 pipes coming out of the muffler(stock), I assumed there are 2 pipes coming into the muffler. Unfortunately, after purchasing a Cherry bomb dual-in dual-out, I learned there is only 1 pipe coming from the engine. Anyway, my question is this. What Y-pipe do I need, and would a dual-in dual-out cherry bomb 2.75″ be risky?

Andy – Definitely don’t want to put a muffler on unless all the ends are capped/attached to a pipe. But beyond that, you can probably hook up what you have and move on (again, provided you weld a cap on one of the intake inlets). The cherry bomb mufflers aren’t exactly restrictive.

So, I will assume the table is gross hp? How much difference does bing off a size make really? If you have 3 inch instead of 2.75 inch, can you wrap the pipe to keep it from cooling down as much to balance out the loss.
I’ve got a V8, DOHC, 4 valve engine makes about ~ 430 hp. I look at it’s exhaust. Which goes goes into 2X 3inch pipe due to headers, then marries back w 2.5, through a resonator and exits as 3.5 inch. You list 3.5 inch as 468. So if my goal is 500 hp, what’s the impact of using a single 3.5 versus a 3.75 pipe? That said, the intake I believe is the problem.

Michael – Don’t understand why you’d have 3″ diameter collectors on the header and not keep that size all the way thru the system. If your goal is 500hp, than you need to go 3″ all the way (whatever your header collector size is).

I have a 2011 silverado 5.3 and had a flowmaster series 40 dual outlet installed; it is 3” inlet and 2.5” outlet. The man used 2.25” inch for the tailpipes instead of 2.5” pipe. Is this enough or do I need to take it back and insist on 2.5”. I called flowmaster and they said it needs to be 2.5” tailpipes for the muffler to work properly. I have noticed their catback systems for this truck all have 2.5” tailpipes, but I have seen other brands and some are using 2.25” tailpipes. I assume all the numbers are outside diameter. My tailpipes are marked 2.25” and inside measures about 2”. Thank you. Danny.

Your manifolds will be the restriction no matter what size of pipe you run (within reason of course), so pipe size is irrelevant. Remember…the closer to the engine you make changes, the more effect you will have. Since manifolds already suck at scavenging (which is why headers are worth so much power on a stock small block chev) replacing them with long tube headers should be your first consideration. Otherwise, forget replacing the pipes with anything larger than what bolts to the manifolds, it would be pointless. You can never flow more than the largest restriction…and manifolds on the SBC are it.

1.5″ primary headers are about ideal for your engine and application (400HP divided by 8 is 50HP per cylinder in a truck, which needs low end torque) but 1-5/8″ is the common size.

The chart above clearly spells out what you need.

2.5 or 3″ collectors merged into a single 3.25″ pipe will be the best solution if you can find it. Duals are REALLY a dumb idea, since they add cost and complexity (both in added components and for working around it) for no benefit. They were ok back in the day that 2″ pipe was all you could find, they aren’t today.

I have a stock 5.7 from a 92 silverado in my 89 Astro van the stock Y pipe is dual 2.5 to single 3 going into a 3 inch catalytic converter then out to a 3 inch sonic turbo then it drops to a 2.5 tailpipe (largest I can find for now) my question is if I put an after market Y in front then another at muffler with dual 2.5 tail pipes will it make enough difference to make it worth it? My goal is to freshen the engine in a year with better cam, intake, and all new bearings etc. I plan on retaining the TBI system all this to tow a camper. Any ideas are greatly appreciated .

Somebody please explain to me why so many factory V8 single exhausts converge their flows at a 90° angle? In other words, a “T” pipe. It’s not even a “Y” !

I have a ’78 Buick Electra with the Buick 350. The driver’s side pipe crosses over and the passenger’s side comes straight down and connects perpendicular! That seems like the WORST way to converge exhaust flows yet, it’s quite common.

Is there some mysterious acoustical or pulsing gas flow physics behind this?
Or, is it because it’s cheap and easy for the assembly line?

Jason,
I’ve been back and forth through this site and many others trying to make sense on how to finish off my custom exhaust. I’m running a 2GR-FE from toyota, 3.5 liter V6. Stock hp is about 270, looking to squeeze about 300 crank or about 255-260 at the wheels. The stock, constricted, crush bent Y/J pipe was swapped in favor of a custom fabricated MKC Y pipe that starts off connecting to the factory exhaust manifold flanges and are 2.25″ on both sides merging into a single 2.5″ flex unit that measures about 6 inches then straight 2.5″ pipe, effectively eliminating the third cat. The factory 24″ resonator links up there and then then the midpipe takes over up until the second merger where the 2.5″ splits back to dual 2″ to the mufflers. The stock setup has two cans out back but is effectively a single exhaust in the middle.
The intake side is already altered with a 3″ CAI, and now that I’ve installed the custom J/Y pipe up front, I need to decide what to do. According to the flow chart, numbers, and max hp per 2.5″ pipe is about 232 hp and 283 for 2.75″ from what I understand. Assuming they are a guideline, are those HP numbers more or less determined as max crank or max wheel hp? I don’t want to overshoot and loose power, as the overall objective here is to gain maximum hp without giving up too much lower end torque. I am planning to keep the resonator to keep the rasp from the V6 in check, I want a throatier-deeper sounding exhaust rather than loud-raspy and annoying.
I was planning to modify the fabricated J/Y pipe up front, by replacing the 2.5″ flex unit at the merger of the dual 2.25″ coming in from the exhaust manifolds with a 2.75″ (70 mm) flex unit and 2.75″ pipe through the next flange and into a custom ordered 7 mm 24″ resonator. I could do this or just do a 3″ flex and pipe back to a 3″ Vibrant super quiet resonator. Since this is where most of the real exhaust tuning takes place and where most hp is achieved specifically at the J/Y pipe up front, should I go 2.75″ or 3″ from the dual 2.25 manifold’s? The other thing thing is the midpipe after the resonator, there isn’t a shop anywhere in Texas that I’ve found with a 2.75″ die for their machine, mandrel bending would have to be 2.25/2.5/3″ respectively, this implies either welding in a cone to gradually decrease to 2.5″ which is oem by the way, or step up to a 3″ midpipe from the 2.75″ resonator with a transition, unless of course if you recommend I do a single 3″ from the flex unit back all the way to this point. The end of this midpipe will merge back from a single to a dual again, where I currently have a unit installed from mandrel-bends.com. These units are top notch as the cuts are nice and clean, without obstructions that cause turbulence. I could do a 3″ to dual 2.25″, mandrel bent 2.25 axleback pipe to my dual inlet outlet magnaflows. The other thing is to leave it all as a single 2.5″ all the way back to the axle back merger and split it off into the dual 2.25″ pipe and magnaflows.
The numbers are clear, I just want your input please, I’ve pulled the trigger on most of these items, part of which are installed, part of which I’ve yet to under hesitation. My gut is telling to do a single 2.75 split in the back to the 2 cans, but I can’t, well unless of course if I get 2.75″ (4) 45 degree mandrel angles and pipe and custom weld the whole thing to make the mid pipe and y merger. Help me please, I need to make an educated decision.

I’m pretty confused by your comment, but I think I can help you anyways. The difference between 2.5″ and 2.75″ pipe is relatively small (~20%) as is the difference between 2.75″ and 3″ (~20%). If you have to go down to a 2.5″ section from 2.75″, you’re not going to run into any performance hindrance unless you’re running WOT. Since 2.5″ is the OEM size anyway, and your vehicle is mostly stock (just a CAI and an engine tune, I assume?), 2.5″ is fine.

I got a Peugeot 205 GTI 1.6 with 105 hp. I am upgrading the head to a model bigger valves that will put me at 115 hp, on the same size stock pipes. I also have a French downpipe that I want to install, which is know to make good horsepower on this car, but the rear end of this downpipe is 2.25″ size. Should I mount 2.25″ pipes all the way back, or should I downsize the pipes with a restrictor to a 2″ size?

Renato – Normally, a 2.25″ pipe is severely oversized for a vehicle with 115hp. However, turbochargers change the rules a bit. Feel free to keep the 2.25″ all the way back, as the concerns about exhaust gases cooling and slowing down are overcome by the forced induction.

Hi Jason – Wow, I read through this entire thread. I commend you in being able to keep your cool while answering, technically, the same questions over and over.

I’ve been researching exhaust for a year and am glad to finally have found some actual demonstrable math and engineering sequences behind this. A lot of my searching has been on mustang message boards and it appears to be many people simply repeating what they read on the internet, without attempting to apply reasoning, science, or hands on experience. After visiting 6 exhaust shops in person, I was met with the same ignorance. And right on par with what I would expect, only 1 mustang owner inquired on this great write-up. With that said, I completely trust your advise.

Now to get to my question:

First of all, I inherited a 2007 v6 (4.0) mustang, which I read has 200 stock HP. Judging from your chart up there, when using dual, my pipes should both be no more than 1 3/4. Magnaflow has a similar chart involving their mufflers: For my engine, using duals, they say the muflfler in/out should be between 2″ and 2 1/4″ (reference: http://www.magnaflow.com/wideopen/performdata.asp) which is different, if ever so slightly, than the pipe sizes on this chart.

Adding to that, ALL of the aftermarket v6 “dual conversions” (Most of the big name muffler companies sell these) come with two 2.5″ pipes. I understand that they say the tests show these pipes to increase high end torque/horsepower, and they market them as doing just that, but being that these pipes go against the mathematical equation, my question is: will using two 2.5″ pipes, or even two 2 1/4″ pipes, really be all that noticeable regarding low end torque. ie: daily driving take offs, in regards to the whole velocity bit?

I just wonder… is it easier for these companies to package the 2.5″ (Most mufflers and tips on the market are easily obtainable and work with this piping size.. as opposed to trying to find something that fits a 1 3/4″!) and feed it to people who don’t bother asking the “whys”… or is it really just such a slight difference in low end torque loss that the average consumer would never notice?

Basically, if the car is a daily driver and has got a 4.0 v6 engine/200 ph, is equipping it with 2.5” piping really all that bad, and if so, what is the motive behind these companies selling their “true dual conversion” kits in that size pipes?

You’ve basically answered it. First, they’re trying to prove horsepower gains, so they’re intentionally designing their system to sacrifice some low-end for some top-end. That way, they’ve got a nice dyno chart to show their customers.

Second, the loss of low-end power probably isn’t too noticeable to the average consumer, who “hears” the power more than they feel it. If you did a series of tests before and after adding the exhaust, you’d probably notice a small increase in 60′ times. But how much I can’t say. I doubt it’s more than 5%.

Three, it’s about packaging. The 2.5″ systems are perceived to be better, so that’s what they offer. Even Ford Racing offers a system this size, which makes me question their product line a bit.

The good news is that these are all cat-back systems, and the most critical portion of the system is from the head to the end of the 2nd catalytic. As long as that chunk of the system is dimensioned properly, things will mostly stay the same in regular street driving.

But if it was me, I’d probably go with a muffler upgrade and save my pennies for a procharger or vortech kit. Imagine the look of surprise on a GT owner’s face when your single exhaust wearing Mustang V6 beats him in the quarter mile. He’s going to feel pretty dumb. 😉

Seems we have a case of the age-old philosophical question, “If a tree falls in a forest and no one is around to hear it, does it make a sound?”

It seems to me that the cult belief of, “Don’t put 2.5 inch duals on a 4.0 mustang, go with 2.25 duals to keep low end torque” is ridiculous. You won’t notice any more low end torque being kept with the 2.25″ pipes than you would with the 2.50″ pipes due to them not only being oversized for the engine, but both also being closely related in diameter to (a) each other, and (b) the recommended 1 3/4″ pipe size.

Simply put I would gather that:
(A) Choosing between dual 2.25″ vs dual 2.5″: slight low-end torque differences between these 2 set ups will be picked up on a dynometer but not felt by typical street driver. Apples to apples. 2.5” is more readily available and comes standard in the kits. No use going out of your way trying to locate 2.25” piping because it will feel the same as using the 2.5”s.

(B) Choosing between dual 1 3/4″ vs dual 2.25″- 2.5″: low-end torque differences will be picked up on a dynometer but not felt by typical street driver. If choosing the larger pipe sets over the 1 3/4” pipes, I would assume that a more experienced/aware person may feel a slight loss in certain take off instances between the two set ups BUT there will also be high end HP gains. 2.5” pipes + bolt ons are readily available and marketed to you due to said HP gains. Low end torque loss minimal and still not felt by average driver, thus, not mentioned to you.

This, IMO, explains why there are no complaints about low end power loss on the reviews/community talk of these 2.5” dual exhaust conversion kits, I just don’t believe it is felt. In the end the customer is happy because, with the larger pipes, they get some high end gains and are able to tell all of their buddies about how they’ve just, “added 10 HP!” to their vehicles.

I look at it like colour shades– Most people would say dark blue is dark blue. But a small margin of professionals (interior designers, for instance) would be able to pick and point out the different blue hues in a single colour spectrum. To their clients.. this is moot and of no interest, as long as they get a beautiful interior to show off. In this scenario, the piping marketers/manufacturers are the interior designers.

Smart marketing, but I can’t help but to chuckle a bit.

Please, please, correct my response in a follow-up comment if I am wrong. I certainly don’t want to feed into any more miseducation on the internet.

I have a 496 8.1 with longtube headers. I run 2- 3″ pipes to a muffler now question is the muffler is dual 3″ in/out but in the center of the muffler its only 1 3″ pipe so do you think of it as a Y but at both ends two Y’s together in the muffler. will that be a bottleneck? Or will it speed up the gasses b/c of the smaller diameter pipe something like the burnelli affect, the truck has about 350-400whp. I just want a free flowing exhaust thats all

I have a 2014 chevy silverado with a k&n filter and custom tune pushing around 320 hp on wheel. I just installed some kooks offroad long tube headers (no cats) and I was considering a corsa sport catback…but I think going 3 inches from the y-pipe all the way to the tip will be too wide don’t you think? Should I just go with a magnaflow or american offroad muffler? or should I look for a narrower catback?

Mudi – The long-tube headers probably make the question academic, as they have a big impact on performance (a lot of truck owners don’t like them because they impact bottom-end performance).

Also, why remove the cats? How are you managing the ECM now – O2 sensor simulators?

There are a lot of moving parts here…you’re asking for advice about something that I would have thought about before I removed cats or added long-tube headers, so my advice is to go find a tuning shop that specializes in trucks and let them advise you. I’m not sure what you’ve done so far is wise.

What is your take for an Explorer with 3.5 ecoboost motor? It is 365hp stock with 2.25″ dual exhaust. I think about 425whp or close to 500 at crank is possible which looks like 2.5-2.75″ pipes. Thinking go 1 size up on a turbo.

Buz – I think EcoBoost motors are fun, but I’m worried about carbon deposits on valves and stalling.

Still, there are a ton of after-market parts for these engines. Pretty sure you can find an extra 100-200hp. That will make your Explorer a hell of a surprise for some unlucky Mustang or Camaro owner. 🙂

I have the opposite dilemma most people have, I’m looking at building an exhaust system for my 660cc three cylinder Daihatsu hijet. The problem is in building something that is not too large. I have sourced the smallest 3-1 merge collector I can find, a 1.25″ into 2″. Will these three primaries be too much flow and reduce my low end torque? Can I step down the output from 2″ down to 1.5″ without issue? I just don’t know the effect of ‘creating’ an expansion chamber directly behind my collector.
Any advice or comments you have would be most helpful…

What r your opinions on catback systems? I have an 08 silverado w 5.3. It has 3″ from the y to the muffler then 2 3/4″ for the tail pipe. Only thing done is a live tune and I opened up the airbox so it can breath better. Been looking at catback systems……but I’m seeing mixed reviews on performance. Some have said theres no noticable difference in performance just good sound…..I really don’t want to spend that kind of money on something if it’s not going to increase performance or mpg….it’s either this or a CAI…..thanks, frank

The closer to the engine you modify the exhaust, the more difference in performance it will make. That is, of course, IF the exhaust is problematic in stock form, and the changes made are beneficial, not negative.

Exhaust is a very complex science. Too much exhaust (in terms of CFM the system can flow) is as bad as too little, but for different reasons.

In the case of factory pipe sizing after the converter? No benefit.

Any modifications made to intake or exhaust airflow MUST be tuned into the PCM unless the system is using wideband O2 sensors…common narrowband o2 sensors cannot modify fuel delivery under heavy load, which is where airflow modifications are most critical to make sure fueling is right.

Frank – I’m a huge fan of tuned cat-back systems (emphasis on “tuned”). But can you noitice a difference in performance? Not with the old “butt dyno”, which is what most people are using when they say that they noticed no difference.

If you just want rumble and don’t care about adding a few HP, I’d suggest getting a muffler only and installing that on your OE system. That will sound great and will cost $200 or less.

I have a ’94 GMC Sierra with a 200HP 305. Originally equipped with a restrictive muffler and a 2/1/2″ single outlet behind the rear wheel. Now it has a Dynomax cat-back system with two 2/1/2″ pipes out of the back. I now realize that this is major overkill for this engine and my style of driving. Muffler has two outlets. Can I remove one side of system after the muffler , weld that muffler outlet shut and use the remaining side? What will this do to my fuel economy? Thank you.

Mike – It could help to weld one side shut. It definitely won’t hurt. The concern I have is about the part of the exhaust system before the last cat…is that original? If so, it’s probably no big deal either way…

This thread is amazing, Thank you for keeping it alive. I have a civic type R fn2 (4 cyl, 2000cc, dohc.. 201 bhp @ 7500 rpm /142 lb·ft @ 5600 rpm) and i’m seeing that many of the aftermarket exhaust are 3″ and only a few are 2,5″. OEM is 2,25″ (with 4 mufflers, lol, NA muted)

The question of what pipe size is better is over and over asked in the forums and most of the people say that the dyno proves that 3″ is better. furthermore, some custom exhaust made by famous tuning workshops of the civic scene are 3″.

so.. why? i have been reading about this a while and i didn’t found any logical reason for a 3″ exhaust perform better in a 2 liter NA engine.

Maybe the people only want to see the peak HP’s in their dyno graphs..or maybe they 3″ do magic..or they are planning to make their engines work between 7900 and 10000 RPM dunno…

as far as i understand, for NA tuning for ~250-260 HP a 2,5″ pipe is better that 3″. More mid-range torque without sacrificing any or only a few top end bhp’s…

Roberto – It’s all about making the peak HP as high as possible. Bigger exhausts sacrifice low-end grunt, but they accomplish maximum throughput at high RPMs. So…the “dyno” says that they’re better, but the race course might disagree. 🙂

The unfortunate truth is that the “import tuner” market is based on marketing hype and what looks cool, not what actually works. Without digging into the specifics (“cold air intakes”, “high flow air filter”, larger throttle bodies, bigger injectors, etc) you are correct in your assumption that the bigger pipe diameter is not helping.

The import tuner market by and large is cluttered with people who have bought into marketing hype, then use that hype to advise others on what is supposed to work best. With an entire community that thinks there is something wrong with the OEM setups that can be cured with a few hundred dollar bolt on pieces here and there, with no analysis, dyno testing, and actual tuning, it is very easy to sell components that are questionable if not downright preposterous.

There ARE good modified import cars out there, done by people that actually understand engines, but the majority of what we see is all about appearance, not function.

Quick question, is the table still accurate when translated to single pipe exhaust? I’ve been looking into upgrading my stock exhaust (single 2.75″ pipe) to headers (LT with 1 7/8″ primaries) and a single 3″ pipe (duals are nearly impossible with my car). I crunched the numbers and found that the cross-sectional area of the pipe would be roughly the same as two 2.12″ pipes. So would my HP be limited to somewhere below 371 (max hp listed for dual 2 1/4″ pipes)?

Oh that must be the “max hp per pipe” column. I guess I figured there might be some crazy physics involved that would make a single pipe produce different numbers than half of what a dual pipe makes. Thanks for clearing that up!

throuly enjoyed article 85 years old but would like little more sound have 2015 kia optima turbo would like kn typhoon and perfomance mufflers any problems has more than enough power!! thank you very much

I want the formulas for calculating the exhaust pipe of a two wheeler, it should contain formulas of diameter of pipe, back pressure, length, etc… We need this calculation for manufacturing a Go-Kart which has engine of a two wheeler….

I have a 74 dodge truck with a 318. We don’t know the exact hp but are thinking it should be near the 200hp range. (318 with comp cam (rv) 4 barrel eddy 600cfm and eddy intake with hooked headers)
We are removing the current exhaust and going to redo it. My mech wants to go easy old school and bring two pipes right back with individual muffler. 2 1/4

I was ok with the 2 1/4 until I read this. I looks like I should be 13/4 and I want to install either and H or X pipe but yet have two mufflers and side dump. Any thoughts ?

Mitch – There’s some room for error in the numbers, especially if we’re talking about older vehicles…the combustion efficiency can very greatly from one to the next, depending on the type of parts you’re working with (basic carb, or EFI conversion? factory heads or high-perf aftermarket varieties?).

I guess I’m wondering if the 200hp figure is too low. But if not, I’d say back things off to maybe 2″ and call it good…you’re close enough on that old truck.

Hello, I have a first gen mazda 3 with the 2.3 litre duratec mazda engine. Stock 163hp. I have vibrant headers installed which are a 4-2-1 design. With the stock exhaust the headers showed a good increase in power, estimated 10 hp. I then installed a 2 1/2 inch exhaust from the catalytic converter back. The stock exhaust was 1 7/8 inches in diameter which reduced from 2 1/2 to 1 7/8 after the catalytic converter. After installing the free flowing 2 1/2 inch exhaust I felt a loss of torque and power across the rpm range. My question is can I install a length of tubing between the catalytic converter and muffler with a reduction is size to say 2 1/4 or even 2 inch. Would this replicate the scavenging effect the stock exhaust had? I enjoy the sound of the free flowing exhaust but miss the low end torque so I don’t want to re install the stock system. Thank you Jason.

Ian, does that vehicle use wideband O2(s)? If it does not, you may be feeling a lack of fuel (lean) under throttle if the exhaust helped.

How far past the converter did they neck it down? Converter adds more heat to the exhaust, so if the necked down portion is immediately after the converter, it may have been a restriction that results in BETTER scavenging now, and a lean condition. But as mentioned, guessing (butt dyno) isn’t real valid to come to good conclusions.

Mike, the mazda 3 from 2006 onwards I’m pretty sure has a wideband primary O2 sensor. Mine is 2007 so I think it does, not 100%. The piping necks down directly after the catalytic converter about a couple inches from 2.5 at the downpipe/catalytic to 1 7/8 all the way to the muffler (stock). Mine is now 2.5 all the way to the exhaust tip.

im doing the exhaust on my 3.6L V6 g8 and i belive the stock pipe size is 2.25 i gonna be running long tube headers with primary pipes at 1 5/8 then a 3 inch collector then H-pipe i was thinking of running the stock 2.25 pipe size with long thrush glass packs would this work good? and support the power im makeing or should i step up to 2.5 pipe?

Christopher – Without knowing a whole lot about what you’re doing, I’d say that you want to lean towards a larger size when optimizing for quarter mile time. Whatever low end torque you lose is more than made up for by better flow at high RPMs, at least as far as time and trap speed are concerned.

Jason, do you mean you don’t recommend shorties except for high RPM performance? The testing I can find shows that long tubes make better power at the low end, but sacrifice some at the extreme upper RPM end of the same engine vs. shorties.

Jason,
I think it’s great that you take time to answer the questions. I’ve read through all the posts and can’t find anything quite like mine.
I have a 1/2 ton Dodge truck with a 440 small block, Indy heads
& intake, larger cam, 2- T60 turbos, huge air cooler. At 12lbs of boost it made 707/685 through an automatic and transfer case and 35″ AT tires.
The exhaust now is a 3″ down pipe from each turbo merged into a single 5″ system. Running 2- 5″ Aeroturbine mufflers in tandem and 5″ all the way out including the tail pipe.
I’m the process of adding a water/meth system with another 5-6 lbs of boost. Do I need a 6″ single or run dual 4″ tail pipes off the present 5″ system? I’m expecting to be in the low 800’s at the wheels, approx 1100-1150 at the crank. I don’t want the wrong exhaust holding me back. Thanks

OK Jason, been reading this blog for an hour & love it. Been fascinated by exhaust for a decade & scooping up all every lick I can.
Quickly, my question’s for a 302 (Low end cam/600 carb) in a ’65 Fastback on its way to Germany to sell one day. Even w/Autobaun, I’m building it for torque/mileage – because they spend as much for a litre as we do a gallon! (k, not quite, but its bad, yea?-lived in Barcelona 2yrs)
High rear axle ratio, so I’m “All about the torque, bout the torque, BIG Bottom!” So LOVIN Small piping!! Just makes so much sense.
So here it is: Ford Tri-Y’s are 1 1/2″, to 1 3/4″ & JUMP TO TWO & ONE HALF!!! Where is the logic in this??? MY best reasoning sz: Cut the Tri/Y’s at the end of the secondaries…& run 2″ all the way to the Bumper!!! (X,H,Muffler,Resonator, even ‘Branch Resonator’ aside. More on this another day: Timing official w/SCCA at Laguna Seca here in Calif. Historic races w/12cyl Vintage Ferrari’s give me wood like nobody’s biz & the closest thing??? “Small block GT350 w/X-pipes, at full song”!!! Don’t Argue, chk ur own wood ;-}~)
Delivered in the kit, is a set of conded reducers: 2 1/2″ to 2″. “D’oh!” I’m not a rocket scientist (but ‘I do play one on TV’) -this just kills me! I just feel Mandrel bends & minimizing expansion/contraction, especially early on’ when exh temp is at it’s hottest/ FASTEST,is the optimum protocol.
K, I’ll quit. Whattya got Jason? throw me a bone, here. -Mike-

Mike – My first question: Is this exhaust setup developed for a specific head? If it’s for the factory head, I’m thinking the size is OK. The 2.5″ tube size is overkill, but it’s far enough back that it’s probably not a big deal. As the exhaust cools and moves away from the engine, the size of the tube becomes less critical. Also, these older engines run rich and don’t necessarily adhere to the table (they’re more likely to come in over than under). They’re not as close to stoichiometric efficiency as fuel injected vehicles.

Mostly, my advice is to find a set of headers that are designed for your specific head. If it’s designed for the heads you have, I think you’re good to go.

Finally, if you want to tinker, you might try putting the reducers on and see how it runs (at least after you’ve got a few hundred miles on the new system.

Currently running a 65mm throttle body, factory MAF. The near future will be a 80mm MAF, 70MM throttle body and ported plenum.

My question: Is it worth the cost to have 2 1/4 or 2 1/5 inch piping made, will it give me any hp increase or anything? I hear 2 1/4 is the right upgrade, then some say 2 1/5 but may lose low end torque.

Robert – If you’re just changing the MAF and throttle body, I’m not sure that an upgraded exhaust is essential. The factory exhaust does a good job of performing both at low RPMs and high RPMs, all things considered. I wouldn’t mess with it unless you’re going to upgrade power in a significant way (new internals, forced induction, etc.).

I just installed a gmpp 350 ho and am adding headman headers to my dailey driver driver truck. I am using duel turbos as well. Considering the motor will be kept under 5700rpm should i go with 2.25 or 2.5 inch pipes?
Thanks

HI,Jason!
Please help me with exhaust diameter for my bike..I have a 988cc engine with 12250 rev limit. The bike put out N.A. 160hp(not wheelhp)@10500 rpm.What diameter size i need to 200bhp@12250rpm?
250bhp@12250rpm?
300bhp@12250rmp?
This size work on the supercharged engine too?
Thank You for the answear
Gabor

I have a 2.5 litre 2006 Altima QR25DE engine that has 2 cats on it. It is a PZEV vehicle built for the California CARB requirements. I got the car 3rd hand and replaced both cats with new after market stock cats along with the 2 O2 sensors and a new stock muffler. I am still scared of the whole problem of exhaust gas getting sucked back into the engine and don’t want to have to worry about that so what header do I get that makes sure that my new precat pipe is larger than my header outlet? Or will I have to get a custom made header. If so how much less in diameter should it be than the precat inlet. I don’t know my precat pipe size.

Alan – Don’t know. My advice is to try and find a complete exhaust system (headers and cat-back) from one company, then model your system after that one. If you find a company selling a header and a cat-back, and they’re using a 4-2-1 collector (for example), that’s the kind of header I would buy.

Daniel – Maybe, depends on how it’s tuned and what you’re trying to do.

If it’s a truck and you really only care about pulling a trailer, it might be too big. If it’s a standard sort of street 440, it’s probably a good size. If you’re racing the 1/4 mile and you’ve got a high horsepower setup (with racing heads, cams, etc.), it’s probably too small.

It is in a truck and will bruised to pull a boat on occasion. It is mainly a weekend toy though. The engine is a 71 block with the original pistons and rings still in it. It has a large cam (probably too big) and closed chamber heads. It has a 600 carb on it, but I’ll be putting a 750 on when i get the chance.

I have 3 vehicles and 2 of them I have done true dual exhaust and I would like to ask you some questions.
1st vehicle is a 93 E-350 with stock 460 BB running 3″ dual after the catalytic converter flang. Should I run 3″ from the header to what I have added?
2nd vehicle is a 2000 S-10 with stock V6 running 2.5″ dual exhaust. This was a put together and I used what I could grab and I was thinking that I need 2.5 from collector to cat when it is 2.25 or 2″.
3rd is a 91 Vic all stock. Should I do 2.5 dual exhaust?

1st vehicle – 3″ tubes for each side of the motor are huge. Can’t imagine it needs that much flow. The chart will tell you what size to put on each side, but I would say that the stock setup is A-OK unless you’ve made lots of modifications.

2nd vehicle – 2.5″ duals are outrageous on a V6 from 2000…way too big. See the table. 😉

3rd vehicle – If you’re going to turn it into a 450hp+ speed demon, than yeah, 2.5″ duals sounds great. But if not, look at the chart in the article.

I know the chart says that dual 2.5″ on the S-10 is to big, but I have had the truck dynoed before and after. All that has been done is pacesetter headers that run into dual cats and dual glasspacks which run on the outside of the frame and dump in front of the tires. The hp and tq before were 141 and 166 and after were 155 and 200. I tend to believe results. I have upgrades that will push the power closer the the 500 mark.

Once I rebuild the 460 BB. It will be a 502 and I will be shooting for 600-750 all motor.

Michael – There’s no substitute for testing – the chart is just a guide. If you’ve dynoed the engines and seen improvements, that’s great. I’ll never argue with data. 🙂

However, I would suggest that you check the HP and TQ output in the low RPM range where you drive on the street. Often times, I see decreases in these lower RPM ranges with over-sized exhaust systems. Headers can often cause this problem too. This is because exhaust gas velocity is better in smaller exhaust tubing at lower RPMs.

If you’re not concerned about the performance at these lower RPMs, than by all means put whatever size you think is appropriate.

Hello, what a great read with alot of helpful info. I’m about to own a KIA Sorento with a 2.2L turbo diesel engine that puts out 147kw/3800 rpm and 441.3nm from 1750/2750rpm.
Test drove the car and its a no brainer for a 7 seater with lots of options thrown in. My only beef with the car is that it feels great off the line but I feel its lacking in the 50mph-65mph range especially when I want to overtake. Based on your chart, its it recommended that I go with a mandrel bent 2.25 inch pipe or should i go with 2.5 inch to increase the performance in the 50-65mph range without sacrificing off the line performance.
Also, from what I read from other sites, some seem to follow the mantra that bigger is always better for turbos as all the effective inertia is used ip by the turbo and getting the the exhaust out asap, allows the turbo to spool up earlier. what are your thoughts on this?
my other option is to chip the car to generate around 245hp and upgrade the exhaust if money was no object lol. now i have to choose between the two.
Thanks for your patience

I’d say that the best way to squeeze more power out of any given diesel is with an aftermarket engine tuner. Air intake and exhaust kits can also help, but engine tuners tend to have the greatest impact on diesels.

Okay I have a question about my 96 bronco. Stock 302. It currently runs a single 3 inch pipe from front to back with a flowmaster 40 series. I bought a 50 series 2 in 2 out 2.25 diameter flowmaster. Realizing that it’s a stock engine, will changing from single to double and downsizing the pipe help me or hurt me?

Hello;
My name is Diego and i’m running an 230 cu inline six cylinder engine. The exhaust system is 6-2-1.
Secondary pipes are around 2″ and the tail pipe after the Y pipe and before the muffler is one 2″ pipe. The car is around 175 horses at 4500 rpm. The engine doesn’t sound harmonic after 3500 rpm and loose power. Do you think the exhaust is too small? Can it cause a noticeable lack of power and bad feeling of the engine?

Diego – A 2″ exhaust for a 175 hp engine might be a bit on the small side. Our chart suggests 2.25″ tubing, but in practice I’d say it’s probably not going to make a huge difference.

However, the loss of power after 3500RPM may or may not be related to the exhaust system. Is the configuration of the manifold the same as it was when it left the factory, or is it different? If it’s a custom setup, it may be that it doesn’t work as well as the OEM manifold it replaced…new OEM manifolds are pretty cleverly designed.

The fact that you say the engine doesn’t sound right leads me to believe there’s something else wrong. A restricted exhaust usually just makes for a weak engine, as combustion efficiency drops off due to a “back up” of exhaust gases. That doesn’t seem like what you’re describing.

Jason;
Thanks for your reply. You are very clear and yes… something else looks wrong. For one moment I thought the exhaust was part of the problem, but your explanation of a restricted exhaust symptoms make the things more clear.

The exhaust is OEM for the original engine of the car with 155 hp, but I upgraded the setup of the engine changing the whole intake of the car with 3 weber DCOE carbs.
This is the same setup that came in the hot version of my car that delivered 176 horses. The only thing I keeped original is the exhaust. In the hot version, the header is the same but the two secondary pipes are 2″ instead of 1″ 10/16 and the tail pipe consist in two 2″ tubes instead of one.
When I made the transformation I thought that my exhaust was good to deal with 176 horses but now…. this is the reason why I’m asking you.
At this moment, the muffler is a round XR1 borla 2.5″ inlet 2.5″ outlet.

Yo i have a v6 pushing around the 500hp it red lines at 7205 and at the time i didnt know about the exhaust and apparently it has 1 1/2 pipe going down the middle and cutting off into 2 2inch pipes does that mean i need a whole new exhuast system

Alex – If you look at the chart, you’ll see a 2″ dual system isn’t completely out of line. A slightly smaller size can really help with low-end torque, and they may have designed your system for streetability.

However, my advice is to ask them to emulate a cat-back system from a well-known exhaust manufacturer (like DINAN or BMW’s M division). If they build your system to match the size/configuration of those systems, great. If not, you can work on them to try and get a change made.

I had a flow master super 10 on my 2010 Silverado before. it was a single to a dual set up. loved it. I have upgraded to a 2016 Silverado 1500 z71. My question is, how do I know what size is running on the stock exhaust as far as the in and out diameter. I am thinking of running dual super 10’s this time and want to order the right size muffler. its much cheaper to just buy the super 10’s and bring them in vs having the shop get them.

very good read and I can confirm correct size pipes was a huge improvement.
I was building a engine exhaust based on my head flow 320cfm from a duratec 2.0l na expected just under 300hp.

I sized the exhaust at 1 5/8 primaries into 3″ collector all tuned length. even tho my head flowed 320cfm I didnt take into account my itb’s only flowed 257cfm with CAI fitted it dropped a bit of cfm as well. On the dyno it made a peaky 5700rpm peak tq to 265hp at 8900rpm and off cam was just bad.

I can’t believe this thread has been going on for 5+years! Thanks Jason! After reading through all of the posts, I don’t think my question has been covered.

I have a 71 Blazer with a 350 SBC that I estimate to be in the 350hp range. I am running an aftermarket ram horn style exhaust manifold that is supposed to flow similar to a header at the lower rpm’s. It has a 2.5″ collector. The chart says 2.25″ dual pipes, but would I be restricting the exhaust manifold. I would consider single exhaust also.

The chart is a good estimating tool, but if you can get within a quarter of an inch of the estimate, I’d say don’t sweat it. Especially on a carbureted 350, which is probably not as impacted by all of this anyways.

Hi – so your are rating by hp? I have a 3.0L turbo diesel pickup, specs are 85hp and 250nm torque, Im thinking of going to a full 2.5″ exhaust system – is this a good size? or 3″? Im considering adding a larger turbo – but not much bigger, Im hoping for around 350nm and 130hp – after exhaust, chipping – if need be a bigger turbo but most likely not..

Francois – The chart isn’t for diesel engines, just for gas. Since most diesels have a turbocharger, exhaust sizing isn’t as crucial.

As far as what to get, I’d suggest finding a performance company that offers a kit for your specific engine. In the USA, Banks and Bully Dog make something for most diesels. Maybe they have something for your engine too.

I am converting my single exit exhaust into a dual exit. My 2015 sonata currently makes 200 hp. My current single pipe is 2.5 inches. Would it be ok to keep the pipe size 2.5 inches when I make it a dual exit exhaust? Should I go smaller when it splits? Can I go any bigger?

Rick – It’s not quite that simple, as crushed bend pipes create a lot of turbulence in specific situations. I’d suggest going mandrel bent whenever possible. Otherwise, you can probably add 1/4 of an inch to pipes under 2.5″. I wouldn’t suggest any changes for pipes over 2.5″.

Hi Jason
Excellent post, my question is for a 1 1/2″ pipe exhaust on a 1275cc BMC engine producing 70 bhp if I’m lucky.
Am I better off fitting 2 x 1 1/2″ x 10″ bullet mufflers in series same size as the pipe or a 2″ x 25″ bullet to the 1 1/2″ pipe?
The area a muffler can be fitted is very restricted 25″ being max, but the longest 1 1/2″ bullet available is 10″.

Dean – You’re right, I did suggest this back in Nov. 2012, and I probably shouldn’t have. The reason is that I don’t know anything about the exhaust gas temps.

If the temperatures are high (and I suspect that’s the case), than exhaust tubing diameter is more important than length. That’s because hot gas moves fast, and fast-moving exhaust can often be dumped into the atmosphere without consequence (like we see on race engines). But, if the gas is cooler, it’s sometimes beneficial to keep it in a pipe. The longer length of tubing keeps gases flowing more uniformly, as the exhaust acts sort of like an insulator.

Thanks Jason, I realise you can’t help, but here is my thought process.

The OE muffler is a baffled 25″ long 1 1/4″ pipe. So I am, as suggested by your chart going to 1 1/2″ pipe, trouble is you can’t get a muffler longer than 10″ in 1 1/2″. Therefore I will go to a 2″ muffler of the correct length, I realise that the gas will expand and cool in the muffler, but it will still be more efficient than the OE setup and I’m hoping will be quieter than 2 very short mufflers of the correct pipe size (10″ includes mounting area, so they are really 7″ mufflers, so 14″ verses 22″). Yes if I could get a 25″ muffler at 1 1/2″ I wouldn’t have asked. Thanks anyway.

Shane – The chart is a good place to start. You can also try testing some different sizes. But the ‘best’ is hard to know without trying things out, knowing more about what you want to do, etc. Please be sure to read the article.

I’ve been looking for an expert and hopefully you can help. I’m running 2″ center dump manifolds due to clearance issues. Im running dual 2.25 pipes. The motor is pushing anywhere from 350 to 400 HP. Would it be worth trying to cram 2.5″ manifolds between the frame , and larger pipes? It’s a street rod 53 Chevy, not a race truck but still would hate to be loosing any significant power. Thx in advance.

Generally speaking, under-sized tubing doesn’t cost you low-end torque: It costs you peak horsepower. If you’re running the 1/4 mile, you can probably increase your trap speed and decrease your time by upgrading the manifolds to something tuned for racing.

But, if you’re just bombing around town, I doubt you’re losing much (if any) power. I’d suggest leaving it be. If you were to upgrade the outlet size and/or add some headers, you might even lose a little low-end torque (only you gain back mid-range and top-end power).

Thank you Jason I appreciate your quick response, the truck runs well and has magna flow mufflers . I would prefer more torque than top end anyways. You have been a great help and a big thank you from all of us for your help.

I have a 2014 Nissan Frontier with a 4.0L engine producing 261HP at 5600rpm and 281ft/lbs torque at 4000rpm factory specs. What would be the ideal tube sizes. I purchased a system to replace it that has 2 1/2″ pipes from both banks that go into a straight through muffler and single exit 3″. My concern is that it is way too loud, and is it too much pipe diameter? What would you recommend? I would like to keep the factory quietness but removed the factory y connection as it is smashed together, I wish I could show you a picture of the factory setup y connector.

Asa – My recommendation is to buy a cat-back system that’s specifically designed for your vehicle. If you can’t do that, than the chart in the post above should tell you what you need to know. But yes, I think the tubes are too big for your application.

Is the factory y-connector damaged, or is it original? If it’s original, it’s probably bent that way intentionally…the shape of the y-connector has a bit impact on the way the exhaust works. Factory exhaust systems often intentionally have choke points, as they can aide with low-end performance.

I have challenger 2010 3.5L V6 .. long tube headers and air system afe and system xforce ( x-pipe .. exhaust ) 2,5″ And it works good on the street ..but I dont like the exhaust sound .. The sound is not high, not huge ,, I am going to change my system exhaust >> bultte exhaust good sound and change the size all system (2.5″ > 3″) I think its good sound .. What do you think bro .?

I have a 2005 Toyota Highlander with a 3.3l engine rated at 230hp@5,600rpm and 242lb-ft@3,600rpm. I have couple of questions regarding exhaust pipe sizing.

The stock system is a ~2.13″ single pipe (likely with a 2.0″ ID although I haven’t checked this). According to your table the ideal pipe diameter is 2.5″. So… I am surmising that the exhaust system is a major restriction here. I also know there is also a pressure activated valve in the resonator that opens when the flow gets high enough – another source of back pressure (to increase low-end torque). If I build a 2.5″ system (since nobody makes one) without a restrictive valve in the resonator I should see a significant improvement in top end power with some loss of low-end torque that I can live with. Would you agree with this assessment?

Second, I am planning to supercharge this engine to about 5 psi which should increase the hp to about 300 (+ or -). Again going by your charts a single 3″ system would be the right size which is where I was headed. Without forced induction I will lose a ton of low end torque and it will be loud. I wondering if I should just go with 2.5″ and call it a day. Despite the small stock pipes, it’s actually not horrible for power although obviously it could use more. What’s your thoughts on this? Do you think 2.5″ will be a major restriction with forced induction?

Glenn – First, yes. The Highlander’s exhaust is probably a bit undersized, as that helps with low and mid-range torque. Increasing the diameter would help the engine breathe better at higher RPMs, but it would probably reduce some of the torque you feel between 1,000 and 3,000 RPM. Also, the top-end gains probably wouldn’t be massive…20hp?

Second, if you’re going with forced induction, you can ignore the sizing and go with what you would like. If you go 3″, it will help a bit at higher RPMs…but the pump that’s pushing air thru your engine (aka your supercharger) is powerful enough to overcome a slightly restrictive 2.5″ system just fine. Heck, it would probably work OK with the stock system.

I’d suggest finding a tuned cat-back system and then build off that. Unless you’ve got the tools to mandrel bend a custom exhaust system, it’s best to go with something purpose built for your application.

Thanks for the feedback Jason. I think I will go with 2.5″ to start. I was thinking the same thing you were that the supercharger will more than compensate for a slightly undersized exhaust. 2.5″ will be cheaper to source and build and I’m sure I’ll be happier with it in N/A form.

I would love to find a ready made exhaust for this car but the only one I could find was by Apexi – it was just the muffler and only 2-3/8″. I’m planning to build a new system from the Y-Pipe back – new cat resonator and muffler. There is really only one bend where it goes under the rear control arms so I will just weld it up from mandrel bent tubing. I guess nobody hot rods Highlanders. I’m really just doing this as a learning experience – the car is 12 years old with 250k km’s on it so it doesn’t owe me anything. If I blow it up no biggie – I was planning on a new car in 1 or 2 years anyway.

my car has 1.3L engine with 1.5″ stock pipe and 82hp. i already installed short ram intake and now i’m planning on doing muffler delete. Based on your chart i must have 1.625″ of straight pipe. I wanna know the effects of loss of scavenging if i made it to 1.75″ or 2″, it’s just that i’m not sure of the available pipes on autoshops near me.

Azmalik – You can ruin the performance of a smaller engine with an oversized exhaust. Unless you’re trying to maximize your quarter mile or track lap time, I’d leave the stock 1.5″ tubing in place.

As for the muffler delete, consider a ‘glasspack’ muffler instead. They don’t really impact performance, but they help with heat retention and improve exhaust gas velocity (at least somewhat). I don’t think I’d recommend completely deleting the muffler, as that could hamper performance too.

If i were to maximize my track lap time would you recommend larger diameter pipe to replace my muffler? And if yes would i benefit largely on 1.75″? Or just replace muffler with 1.5″ pipe?

I’d be racing for some recreation time with my friends. I want my small engine car to be balanced (don’t know the appropriate term). Like when i need power then it’s always there (reduced backpressure) and if it’s just for city driving won’t lose the scavenging effects due to increased diameter.

Hi Jason.
Great to see someone sharing information without advertising specific brands.
I need to replace a system, and am very surprised by your chart and comments.
The engine is a 215 ci Rover V8 (ex-Buick), with a few mods, developing aprox 230hp. I currently have a dual 2&1/2 system with a balancer tube of the same size. The car also have headers.
Question: I am partial to balancer tubes, but would like to hear your opinion. (no space for fancy x-type mixers)
Looking at your chart, my current set-up is overkill??
Would you recommend dual 2″ and what size balancer?
Thank you for easily understandable answers- here in South Africa its always a “bigger is better” viewpiont
Regards
Johan van Wyk

Johan – Balancers aren’t really useful on V8s, as far as I’ve seen, as both sides of the engine are in balance anyways. Balancers are nice when you’ve got a V6, but beyond that, they’re mostly used to try and pull out the higher frequencies in the exhaust note. You can accomplish that with a good muffler, so I’d suggest saving a little money and getting a system without a balance pipe.

Hi I have a 2002 s10 with a 355 making 425hp. I am wondering how this calculation works when you run a single pipe back with duals out. I don’t have room for true duals so im looking at single 3 inch into a flowmaster super 10 after the rear end with 2 2.5 tail pipes would this be sufficient flow. Truck is just basically going to be street driven. Thanks for you help

Excuse me , I have Peugeot 406 4 cylinder 2000 cc , the back box got damaged , I have a friend offered me a muffler but for Peugeot 406 6 cylinder 3000 cc , what is the effect of this box if i fix it on the torque , fuel consumption and noise ?
Regards

hello, i have a TB chevy 2006 LS 4.2 i want to change just the muffler ( flowmaster 50 delta flow) 2.25 in_ 2.25 out , the factory diameter are 2.3/4 if i reduce 0,5 it will affect the performance? thanks

Jason Thanks for your quick reply so what I understand is that reducing the half inch muffler does not affect performance and vilocity ?,
about the muffler that is on my chevy it is original manufacturer 2.5 inch out _in

Hi,and greeting from Germany!
Have a 1969 Dodge Charger,510 cu inch 550 hp.
Dual Eaxhaust.Which Muffler are the best for a good flow and agressive sound?
Will install a 3″ stainless Exhaust system.
Is Flowmaster 40 or 44 or magnaflow,or what ever the best?
Please help me.
Very Thanks.

Hi,greeting from Germany again!
Jason,is the 2,5 inch Dual exaust system enough for 510 cu inch(550 hp),or better a 3″ pipe and muffler.Need a new one.
Looking for much hp and loud agressive sound of my 69 Charger.
I have a bad 2,5 inch System with lots of neck`s.
Can you help me.
Thanks

Hansel – A dual 2.5″ system might be a bit small if you had a modern engine, but I think you might want to keep it on your old 69′. Increasing tube size will get you more horsepower, but it won’t be quite as fun to drive on the street.